These suicidal maniacs might be willingly infected with a horrible germ or virus: smallpox, ebola etc, then let loose in crowded airports etc to infect as many as possible.
Some of these, such as anthrax, have a fairly long infectious stage before symptoms set in, long enough to set off a chain reaction from airport to airport to airport.
In my research on Hybridon ,I came up with the goodie that Mahfouz owns "Med-Emerg International, Inc, whch owns clinics in Canada, 2 of which are walkins in Torontos Pearson Airport!
May all your infrastructure be ours!