There is a question that has crossed the mind recently of anyone who has sent a cell phone text message while cheating on a spouse: What was I thinking?

Text messages are the new lipstick on the collar, the mislaid credit card bill. Instantaneous and seemingly casual, they can be confirmation of a clandestine affair, a record of the not-so-discreet who sometimes forget that everything digital leaves a footprint.

This became painfully obvious a week ago when a woman who claims to have had an affair with Tiger Woods told a celebrity publication that he had sent her flirty text messages, some of which were published. It follows on the heels of prominent politicians who ran afoul of text IQ, including former Mayor Kwame Kilpatrick of Detroit, who went to prison after his steamy text messages to an aide were revealed, and Sen. John Ensign of Nevada, whose affair with a former employee was confirmed by an incriminating text message.

Unlike earlier eras when a dalliance might be suspected but not confirmed, nowadays text messages provide proof. Divorce lawyers say they have seen an increase in the number of cases in the past year where a wronged spouse has offered text messages to show that a partner has strayed. The American Bar Association began offering seminars this fall for marital attorneys on how to use electronic evidence — text messages, browsing history and social networks — in proving a case.

Although most e-mail users have come to understand that messages remain on their computers even if deleted, text messages are often regarded as more ephemeral — type, hit "send" and off it goes into the ether. But messages can remain on the sender's and receiver's phones, and even if they are deleted, communications companies store them for anywhere from days to a few weeks.

Lawyers expect the number of cases to grow as younger cell phone users, who are more likely to text than talk, marry.

At the root of the issue is the increasing lack of privacy in our show-and-tell digital culture. Text messages are considered private, much as telephone calls are, legal experts say. But if a cheating spouse's cell phone is part of a family calling plan or regularly left unlocked and unattended on the dinner table or night stand, it is conceivable that a partner who suspects infidelity could make a case for sifting through the in-box.