tonight on "world news," terror plot. explosives bound for chicago intercepted in england and dubai. how did the plot unfold, what was the device? and what will the u.s. do to stop dangerous cargo? final four. the whirlwind last four days of the campaign and the president is pushing hard. the republican who would be speaker is speaking out. and, sweet inspiration. a man has a great idea to help others this halloween, and he's our "person of the week." good evening. it was meant to be an attack. it was meant to do harm. tonight, the white house has made it clear, terrorists have tried to target the united states again, this time, chicago.

packages of explosive materials sent from yemen on cargo planes. they were intercepted. the president informed of the threat late last night. this afternoon, he spoke at the white house. >> last night and earlier today, our intelligence and law enforcement professionals working with our friends and allies identified two suspicious packages bound for the united states. an initial examination of those packages has determined that they do apparently contain explosive material. >> and our homeland security team has been following this story all day. chief investigative correspondent brian ross is in washington tonight and brian, we'll begin with you. >> reporter: diane, with the help we're told of the saudi intelligence service, the u.s. learned late last night that al qaeda in yemen was trying to ship at least two bombs to synagogues in chicago in separate air cargo packages. the explosives cleverly hidden in printer toner cartridges.

within minutes, u.s. officials orders every plane with any package from yemen to be intercepted and searched. the packages were sent from yemen to chicago by fedex through dubai and the other by ups through england. early today, british authorities at the east midlands airport, north of london, seized a large box with a printer, whose toner cartridge appeared to have been tampered with. loaded with almost a pound of white powder, where there should have been black powder. the president's lead counter terror adviser said it was an explosive compound that officials said was going to be somehow detonated by a cell phone. >> they were not letters. they were larger than that, think about bread boxes or so in terms of size. we don't know yet how they were intended to be activated. >> reporter: officials believe the powder may be the homemade highly explosive petn, used in the failed plots by the so-called shoe bomber and the underwear bomber.

even a small amount of petn can cause huge damage, as seen in this demonstration. early today in chicago, fbi agents warned jewish community centers and synagogues to be on alert. as possible targets of al qaeda. >> clearly, they are looking to identify vulnerabilities in our system. and take advantage of those vulnerabilities. there's nothing about al qaeda that surprises me anymore. >> reporter: the discovery of the two bombs set off a scramble to inspect every package and many flights coming from yemen. late today, two f-16 fighter jets escorted a flight from dubai as it landed at kennedy airport in new york. earlier, authorities in newark and philadelphia searched ups and fedex cargo jets thought to be carrying packages shipped from yemen. and in new york city, police actually intercepted a delivery truck believed to be carrying a package that had originated in yemen. no explosives were found on the truck. u.s. officials are hardly resting easily tonight. shipments from yemen to the u.s. going back weeks are now being

examined as fbi agents in chicago and cia officers in yemen seek to find the individuals involved in this latest foiled plot, diane. >> well, brian, as you reported today, at one point, we heard as many as 15 possible packages could be out there. what's the word on that tonight? >> reporter: well, the latest intelligence that was received last night was that there could be as many as 15 of these packages being sent, essentially printer bombs. that's why now the scramble to search all these flights and go back and look at the records of all the packages. so far, only two have been identified as having explosives, the two grabbed in dubai and england. >> so, there's no evidence of the others tonight? >> reporter: there is not tonight, that's correct. >> all right, brian. as you saw earlier, everyone at home, the president did appear before reporters. it was a brief, sober statement. jake tapper, our white house correspondent, was in the room. jake? >> reporter: good evening, diane. it was at 8:00 a.m. this morning when white house officials decided to require the inspection of all packages coming into this country from yemen.

just one decision of many made throughout a frenetic night and day. a press conference called at the last minute. with a message to the american people that his team is on the case. >> the american people should know that the counter-terrorism professionals are taking this threat very seriously and are taking all necessary and prudent steps to ensure our security. >> reporter: the president was in the white house residence last night at 10:35 when his top counter-terrorism adviser john brennan e-mailed him to tell him about credible intelligence of a plot to send bombs from yemen to chicago. >> anybody who is associated with al qaeda is a subject of concern. >> reporter: keeping in e-mail communication with the president throughout the night, brennan sounded the alarm. at 11:00 last night, he held a conference call with top officials of the cia, fbi, department of homeland security and national counter-terrorism center. at 1:00 a.m., intelligence officials, the state department, the faa and military officials of the u.s. northern command at

peterson air force base in colorado. at 9:00 a.m., brennan talked to the president of yemen, who brennan has met with four times in the last two years. at 10:15 this morning, president obama was briefed in person by on the threat by top officials, in the oval office in the morning and later in the situation room. tonight and tomorrow, the president will hold a series of rallies for the midterm elections across the country, and will spend the night in his home in chicago, where the first lady has been all day. across the street from a synagogue, though not one of the two targeted, according to officials. diane, the president will continue with his campaign schedule despite the terrorist threat. the white house says the president is continuing with his plans and the american people should continue with theirs. diane? >> so, he is going to chicago and joining the first lady who is already there. >> reporter: that's exactly right. he'll start in virginia and he does cleveland, chicago, philly, bridgeport, he's continuing as if the threat is not there. >> thank you, jake. and, as you know, the planes intercepted in england and dubai

did set off a wave of security sweeps on cargo planes at some of the busiest airports in the country. and today's plot highlights the vulnerability of the whole cargo system. 1,000 planes carrying cargo of some kind fly into the u.s. every day. our senior justice correspondent pierre thomas on the new measures tonight. pierre? >> reporter: diane, tonight, u.s. officials are deeply concerned, this is the fourth al qaeda plot targeting u.s. soil in the past 13 months alone. abc news has learned that tonight, officials at this secure, secret location outside of washington are tracking every package coming from yemen. >> we cannot let our guard down for one moment. they are coming at us 24/7. >> reporter: in response to the potential threat, today, fedex cancelled all cargo flights emanating from yemen. and the department of homeland security warned americans they would be seeing heightened security measures in the coming days, including more passenger patdowns and expanded random checks for explosives.

>> even though it's not on the front pages, al qaeda is still as active and as intent as ever. >> reporter: every single piece of cargo aboard u.s. passenger flights is screened. but that is not the case on cargo-only flights. screening on those flights is targeted, based in part on something that triggers suspicion. that is precisely why terrorists may have decided to target cargo flights. >> they believe that cargo planes would not be as secure as passenger planes. and they're probing. there's always -- al qaeda and all its elements are always trying to find weaknesses. >> reporter: sources say the terrorists may have mailed the bombs because they believe it is more difficult to obtain explosives in the u.s. >> al qaeda is able to, for example, build a bomb in yemen or in pakistan or in afghanistan. they have access to the destructive materials. they don't have to actually bring a person into the united states or rely on an operative in the u.s.

what they're doing is relying on the mill service and trusting that the package is going to get there in the way that the courier says it's going to. and that, unfortunately, in a case where a bomb goes off, is a very bad delivery. >> reporter: u.s. officials believe that al qaeda is desperate to hit the u.s. before the tenth anniversary of 9/11, and that's less than a year away, diane. >> but you're saying they're targeting yemen specifically. how do they know whether or not to target other countries in the region? >> reporter: diane, that's the big question tonight. is yemen the only location that packages may be coming from? they just don't know. so, right now, they're going over other security measures that might be taken. that is the operative question tonight. are there other locations other than yemen that the packages might come from? >> pierre, thank you for your reporting all day long. and speaking of yemen, martha raddatz, our senior foreign affairs correspondent, was the first western television journalist to enter yemen after the attempted airline bombing last christmas day to investigate al qaeda and the terror trail there.

and also joining us, top terror expert richard clarke, a former white house counter-terrorism official and now abc news consultant. dick, let me start with you. how many al qaeda do we think are in yemen and are they different from the al qaeda in pakistan? >> diane, we think there are about 500 or 600 al qaeda in yemen, which is three times the number of al qaeda in afghanistan. even though the united states has 100,000 troops in afghanistan, and no troops in yemen. they are somewhat different. but they are probably controlled by bin laden, remotely, from wherever he is. >> and i know you've talked to the counter-terrorism officials you know so well. what did you sense from them today about the degree of this plot? >> this is a very serious plot. they were on it quickly and they had good luck. but this means they're going to have to step up their efforts against al qaeda in yemen and yemen is a government that's friendly to the united states,

but it's a weak government, and it's been unable to stop al qaeda. >> well, martha, you were there. we watched you on the terror trail in yemen. and, there's a name that's come up over and over again in these terror plots and it's anwar al awlaki, born in new mexico in the united states, he was an imam in california and virginia. tell us about him and al qaeda there as you saw them. >> he is a top target of the cia and the u.s. military right now, diane. and that is extraordinary, to have an american targeted. believe me, if they can find him and they can't capture him, he will be a dead man. they have been striking yemen over the past year with u.s. cruise missiles, ship-launched u.s. cruise missiles. last december, in january, in march, going after these terror training camps, where they believe abdulmutallab trained. >> and what are you hearing at the defense department tonight? are they going to step up these attacks? >> well, they've been trying to step up the attacks for a long time.

they are really concentrating on this country. and if they find a direct tie, you can bet there will be more attacks. >> richard, are you expecting more attacks? >> i think we'll see more cia operations in yemen and as martha said, if they can find targets in yemen, you'll see more cruise missile attacks and more predator attacks by the united states. >> all right, richard clarke, reporting tonight for us and martha raddatz, as well, and, again, thank you both for weighing in tonight, and all day long, as well. and still ahead on "world news," four days, final push. what were the big campaign developments today? and in your neighborhood, the surprising new face of a serious addiction in america. and just in time for halloween, a man who turns all that leftover candy into a smile for american troops. our "person of the week." ♪

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and other news today. four days to go before those midterm elections. and in the home stretch, democrats and republicans are staking out their final positions. democrats looking to keep some open doors in congress. republicans trying to close down the options of one man, president obama. jon karl has more. >> ladies and gentlemen, the next speaker of the u.s. house of representatives -- >> reporter: stop obama. that's the message from would be speaker john boehner tonight in ohio, as he begins the final push. >> your government is out of control. do you have to accept it? do you have to take it? hell no, you don't. >> reporter: in race after race, republicans are closing out the campaign by trying to make tuesday's elections into one big national referendum on barack obama and the democratic leadership in washington.

exhibit a -- this new ad by tea party republican sharron angle in nevada. >> skyrocketing bankruptcies. they promised change. now, it's our turn. >> reporter: as for the president, "the daily show" aside, he's been off the campaign trail for three days, and today visited maryland, one of the few states where a democratic senator has a big lead and needs no help. and that senator didn't even bother to show up. >> barbara mccculskey couldn't make it but wanted me to say hello on her behalf. >> reporter: across the country, embattled democratic candidates are closing out with personal attacks. some of them down right brutal. >> guns. prostitution. murder. >> the felts. the state. charges that he ripped off clients. and he used it for prostitutes. >> lawyer, lobbyist, convicted criminal.

>> reporter: a new study of campaign ads finds that more than half of negative democratic ads are personal attacks, whereas the overwhelming majority of republican ads attack democratic policies. as for the president, he will be out on the campaign trail again tonight, trying to save embattled house democrat tom perriello in southern virginia. if he can do that, save that one seat, diane, at least they would have a glimmer of good news for democrats on election night. >> three more sleepless days to try to pull it out. thank you, jon karl. and coming up on "world news," one suburban family, one daughter, 100 hits of heroin a day. desperate for nighttime heartburn relief? for many, nexium helps relieve heartburn symptoms caused by acid reflux disease. and for the majority of patients with prescription coverage for nexium, it can cost $30 or less per month. headache, diarrhea, and abdominal pain are possible side effects of nexium. other serious stomach conditions may still exist. ask your doctor if nexium

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to get one month free, plus more tips, visit boniva.com or call 1-800-4boniva. we have a progress report on the u.s. economy. we learned today the quarter beginning in july saw 2% growth, fueled by consumers spending again, particularly businesses restocking their shelves. economists say this also means a double-dip recession is now highly unlikely.

but there is a shadow. traditionally job growth doesn't kick in until the gdp grows 3% to 4%, and the u.s. is stuck at 2%. and, a program note. all of us at abc news have been bringing you a series of snap shots of america's new suburban epidemic. in the past three years, the number of heroin users has nearly doubled. half of all first-time users are younger than 26. "20/20" anchor chris cuomo and his team have been visiting family after family around the country, trying to deal with what is an increasingly potent drug, and one family with their own daughter. >> i'm literally just rotting. >> reporter: hopeless at only 21 years of age. ashley is in the grip of a killer. heroin. >> i think when people look at me, i mean, they see i live in a really nice house and that i don't look like a heroin addict. >> reporter: this is not supposed to happen to you.

too smart, too many people who love you. too much money and potential. >> i never thought in a million years that i would be that kind of person. >> reporter: the one-time college student is now holed up in a basement room she calls her dungeon. and this dungeon is not some squat or abandoned house. she lives in her parents lovely suburban home. parents who love and care about their daughter but don't know what to do. >> right now, you act like you're high or something. >> if i could stop, i wouldn't have gone as far as dropping out of school, quitting my job, being sick every day. it's a horrible life to live. >> but we think you'll want to see what happens next, for that young woman, and her family, after chris's report. something that gives you real hope, and you can see it all on a full hour of chris cuomo's reporting tonight on "20/20." coming up, how this man is making our soldiers overseas smile, one snickers bar at a time.

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hallowee he is our "person of the week," and dan harris has his story. >> reporter: for children, it's the sweetest holiday. but for dentists, halloween can be horrible. >> normally, you wouldn't put your child in front of a shopping bag of candy and say, go ahead, have it. when you have childhood decay on the rise and obesity is almost of epidemic proportions, halloween is a brand new nightmare. >> reporter: so, chris kammer, a dentist from wisconsin, came up with a creative solution. >> two pounds. >> reporter: he offered to buy back his littlest patients leftover loot for $1 a pound. >> this is all yours! >> can you say thank you? >> thank you. >> reporter: halloween is americana. kids are going to go out and they are going to trick or treat. we understand that. we'll buy back the candy that sits around all week that they just don't really want, but they'll eat it because it's there. >> reporter: initially, even his own kids didn't believe he'd be

able to get trick or treaters to part with their candy. >> when i first shared with my own kids, they said, dad, that's a terrible idea. >> reporter: his kids, however -- >> there you go. >> reporter: were wrong. >> four pounds! >> reporter: dr. kammer's simple idea has now become a national movement. the halloween candy buy-back program. with more than 2,000 dentists registered to participate in almost every state. and the amount of candy they've been able to collect is astonishing. 122,000 pounds last year alone. and what happens to all of it? it gets shipped to the troops overseas. >> to the troops, i think the candy is a remembrance of home. i want them to know that we haven't forgotten about them. that little children are out collecting candy for them. on halloween night. >> reporter: the troops give most of the candy away to local children to build relationships. as we said, dr. kammer's idea is simple, but it's having a global impact and teaching kids here a lesson about health and giving. >> gives you that warm feeling you can't describe.

but i think that's why we all live, for that warm feeling, to help each other. >> so, for truly happy halloween, we choose chris kammer. he says as a child he watched his father give back to the community, and that's what inspired him. and if you want to find dentists near you who are participating in the program, they're on our website. check it out. we, of course, will learn more about all the breaking news of this day. we want you to know, you can count on abc news online and through the weekend. but for all of us at "world news" on this friday, have a good weekend, and we hope a very good night. good night. tonight from 7 on your side moral dilemma facing thousands of homeowners. should you walkway from your

mortgage snoo how vulnerable are bay area airports? the biggest pull in airport security. >> republican karly fiorina in the senate race y these comparing herself to democrat dianne feinstein. >> and the giants depart for game three of the world series in dallas. live from texas with fans at home, expecting them to sweep. it just doesn't get better than this. inside at and t park, fans going wild. giants claim their second victory at game two of the world series. >> good evening, game three is tomorrow afternoon in dallas. the team boarded buses outside at ask t park