If you are getting divorced or in a custody battle, you might want to delete your Facebook page.

According to a February 2010 survey of the American Academy of Matrimonial Lawyers (AAML), 81 percent of divorce attorneys said they have seen an increase in the number of cases using social networking evidence during the past five years. Facebook is the unrivaled leader for online divorce evidence with 66 percent citing it as the primary source. MySpace and Twitter were a distant second and third, at 15 percent and 5 percent.

The evidence is not always showing that a spouse is having an affair, as all states have no-fault divorce laws. No-fault has made it rarer to divorce on grounds such as adultery or cruelty. But the effect of those laws varies widely, and affects how useful evidence from a social networking site is. 

In South Carolina, for instance, one can still file for divorce on the grounds of adultery, and that can affect alimony payments, says Melissa Brown, a family attorney in Charleston.

It could affect credibility, she said. Like if there were pictures of you doing drugs around kids, it could affect visitation. Assets are another issue that comes up. Sometimes they will say I don't have any money and then go bragging about new yacht or trip to Italy.

Brown notes that she advises her clients to make sure they delete Twitter pages if they can, or at least make sure as much as possible is private on their social networking accounts.

There is the problem of counterfeiting evidence as well. Making sure that if you see something on the Web that could be evidence in a legal proceeding is authentic is important. Creating a PDF file is a good way to do this. 

At Blank Rome, attorney Leonard Florescue agrees the issue of adultery in divorce cases -- at least in New York -- isn't as important as it once was. Plain old adultery just doesn't raise a lot of hackles with the court, he said. The bigger issue is keeping clients from playing amateur detective.

Using the Internet to spy on a spouse can be a big problem -- for the one doing the spying. In any situation where there is a reasonable expectation of privacy, unauthorized access can be a violation of the law and open one up to criminal charges.

One example is a computer used almost exclusively for work that one's spouse would not usually have access to. If someone breaks in to look at their Internet activity, that would be inadmissible. The same holds true for hacking Facebook accounts.

How much evidence a divorce or family attorney will use from a site such as Facebook also depends on how relevant and authentic it is. Given that photos can now easily be altered, a picture someone posts on their page isn't the ironclad evidence it used to be. You can't really trust photos anymore, he said.

While embarrassing photos can sometimes be a problem, Florescue says he has seen situations where such evidence was shot down by the judge. In one case, a man had photos from a party that showed him getting drunk. The judge said, 'you were there at the time -- didn't you marry him?'

The best remedy, both lawyers said, is to be more careful about what you put on the Internet. Florescue says his clients are usually sophisticated enough to know better, but that isn't universal. Yes people go there, Florescue said. Yes, people post things that they shouldn't.