Even how long many planned to stay in the United States and where.
Before Sept. 11, that was rarely the case, reports CBS News Correspondent Jim Stewart. Before Sept. 11, the FBI focused almost exclusively on investigating crimes and terrorist incidents that had already occurred. Now the bureau's focus is on preventing terrorist incidents before they happen, and that means a change in the way it does business.
Take wiretaps, for example. A little-known court on the sixth floor of the Justice Department secretly hears all FBI terrorism wiretap requests. Bob Blitzer, former head of the bureau's anti-terrorism effort, thinks last year the bureau filed well over 1,000 requests - a new record.
"I think information is more important than evidence because information can lead to prevention," said Blitzer.
And the FBI has some new tools to get that information, as Mafia bookie Nicky Scarfo found out the hard way.
The FBI had fitted Scarfo's computer with a top-secret device that monitored what he typed as he typed it, exposing his entire bookmaking operation.
Privacy experts were stunned to learn the bureau even had such bugs.
"We've moved away from the era of alligator clips on the telephone wires to very sophisticated, high-end surveillance techniques that are classified and the details are kept from public view," said David Sobel, a privacy expert.
To understand what foreign suspects are saying on wiretaps, the bureau is hiring hundreds of translators.
And the same undercover teams of disguised FBI experts who took film of a Russian spy are now being used to watch and follow people tied to terrorist investigations.
The hardest part, lawmen acknowledge, is knowing who to follow in the first place. In January alone, 740,000 foreign nationals arrived in this country every single day.