The newspaper said that when an employee of a McLean, Va., investment firm used the file-sharing software LimeWire to trade personal files with other users, he exposed the Social Security numbers and birth dates of 2,000 of his clients, including that of U.S. Supreme Court Justice Stephen Breyer, that were stored on his computer.

The security breach wasn't discovered for six months until it was discerned by a Washington Post reader and brought to the newspaper's attention.

People looking to share music, movie or other kinds of files use peer-to-peer networks to link computers directly without the need of a central Web site to manage the exchange. Computer security experts, however, say many users aren't aware that some such programs allow access to a portion, if not all, of a user's documents, the Post said.

"To me, this was devastating," said Phylyp Wagner, founder of the investment firm, Wagner Resource Group. "I didn't even know what peer-to-peer was. I do now."