Instant-messaging conversations, though quick, aren't always fleeting — as proved by the digital trail of U.S. congressman Mark Foley's salacious chats with teenage pages that emerged last week and forced the Florida Republican to resign.

ABC News, which broke the story of Foley's instant messages (IMs) and e-mails from 2003, has said former pages were the source of the revelations. Most likely, the pages who corresponded with Foley either manually saved messages or used IM software with built-in logging capabilities, allowing time-stamped chat sessions to be kept indefinitely on one's computer.

The programs vary in whether the features are initially on or off and how well they notify users.

"Computers are really, really good at saving things, unlike a dumb telephone," said Richard M. Smith, an internet security and privacy consultant at Boston Software Forensics.

"If you don't want something to get out, don't put it in any computer form at all."

Can turn off logging on some IM programs
 
Chat programs from Yahoo Inc. and Microsoft Corp. are among those with logging capabilities. Microsoft's installs with the "off" button initially selected, while Yahoo's automatically records chats but clears them when a user signs off. (Users can choose to turn it off or record forever.)

AOL Instant Messenger, the most popular IM service in the United States, doesn't offer logging in its current consumer versions but does in its business-oriented AIM Pro software. AOL's service also can be accessed by Trillian and other third-party software with built-in logging.

Computer-indexing programs such as Google Desktop also have options to retain chats on a personal computer. Some computers also may have keystroke-recording programs secretly installed by a boss or a spouse.

In some cases, the services themselves retain chats.
 
Google Inc. offers users the ability to store such conversations online, so they can be accessed just like e-mail. You need a password to see conversations, although Google and other service providers typically disclose such information to law enforcement when issued a subpoena or court order.

Time Warner Inc.'s AOL, Yahoo and Microsoft all say they do not retain chat sessions at all. Once a message is sent, it should exist only on the sender's and recipient's computer.

Attorney General wants law preserving records

The Foley investigation comes as U.S. Attorney General Alberto Gonzales seeks a federal law requiring that internet providers preserve customer records, asserting that prosecutors need them to fight child pornography. However, Justice officials have said that any proposal would not call for the content of IM and other communications to be preserved.

Some employers have software in place to record traffic through their networks, and some business-grade IM systems have centralized logging.

'Delete does not mean delete, and a hard drive by its very function is going to retain all sorts of information about a person's computer that they may not be aware of.'-Kristin Nimsger of Kroll Inc.'s Kroll Ontrack

Conversations may also remain on Foley's home or work computers, even if he did not have automated logging. Some computers temporarily store their memory's contents on the disk drive, but the data could take awhile to get overwritten, said Kristin Nimsger, vice-president of legal technologies with Kroll Inc.'s Kroll Ontrack.

"Delete does not mean delete, and a hard drive by its very function is going to retain all sorts of information about a person's computer that they may not be aware of," she said.

The Justice Department has ordered House of Representatives officials to preserve all records in the Foley case.

The tougher part may be proving the messages' authenticity, particularly when the evidence comes from the recipients. Logs are generally plain text files that can be easily altered.

Mark Rasch, a former Justice Department computer crimes prosecutor, said prosecutors must also prove that Foley was on the other end, not someone else using his IM account.

"We've got to prove that the instant-messaging session occurred and that Foley's hands … [were] on his keyboard," Rasch said.