The action came nearly three and a half months after a heighten state of alert was imposed based on the discovery of computer records in Pakistan.
Because he was the Qaeda figure most directly involved in the reconnaissance, the fact that Mr. Hindi was at large was seen as highly worrying to American officials last weekend, after the discovery of computer files in Pakistan first provided the Bush administration with information about the scope and sophistication of the surveillance.
Bad news: As lawyers increasingly demand discovery of computer as well as paper records, this particular form of legal torture is getting even worse.
But there is no better evidence of Al Qaeda's search for everyday targets than the discovery of two computers once used in a Qaeda office, a desktop and a laptop, that were later purchased by a Wall Street Journal reporter from a computer merchant in Kabul for $1,100.
Those suggestions were based on the discovery of a computer belonging to Salah Abdeslam, the only surviving member of last November's Paris attacks.
And they wouldn't have been, he added, but for a search warrant and an F.B.I. technician's discovery of a computer password.
The investigation followed the belated discovery of the computer error at the Northern general hospital in Sheffield, where tests on samples from the women started on January 4 last year, less than a week after the NHS's intensive anti-millennium bug preparations for 2000 were completed.
Five days after a computer security firm disclosed the discovery of Gauss, a computer virus targeting computers in Lebanon, they issued a cry for help.
Two senior NASA officials also reported the discovery of a flight computer, only to declare later that it was an avionics box, and today that it was an antenna.
The suspect, known as Abu Issa al-Hindi, was described by the officials as by far the most important Qaeda figure detained as part of an American-led effort to unravel the tangle of clues uncovered with the discovery in Pakistan of computer files containing the surveillance reports.
