According to a PCWorld report, this morning a bug in Google Talk resulted in the incorrect sending of instant messages, exposing private chats to the wrong recipients. Google supposedly acknowledged and resolved the problem in about three hours, but it may have been longer, according to users.
"But judging from the frantic and horrified messages posted by affected users in discussion forums and social media outlets like Twitter, the bug may have been active for about five hours."
It's uncertain how many users were affected. You can read the story in full by clicking the aforementioned link.