Hackers infiltrated powerful supercomputers at colleges, universities and research institutions in recent weeks, disrupting one of the nation’s largest online research networks for several days and raising concerns among computer security experts that the compromised machines could be used to attack specific Web sites or parts of the Internet. As many as 20 institutions were targeted, according to two sources who work at facilities affected by the attacks. Both asked that their names be withheld because they are aiding the ongoing investigation and fear that officials at other institutions may refuse to cooperate if they believe they could become the subject of media coverage. Full Story