A study carried out for a divorce website claims Facebook was named in at least 20 percent of divorce petitions in the US this year. It appears many people are having inappropriate chats with people they were not supposed to.
And the most common reason is spouses engaging in saucy sex chat with their online "friends".
Other social networking sites, including MySpace, Bebo and Twitter, also featured heavily in the sample of 5,000 divorce papers studied.
Mark Keenan, who carried out the research for website Divorce-Online, said: "I had heard from my staff that there were a lot of people saying they had found out things about their partners on Facebook so I decided to see how prevalent it was.