14 Boston-area law enforcement agencies, and over half revealed that they use social networking sites to collect evidence ranging from discussions of illegal activities to photographic evidence of crimes including underaged drinking and vandalism. The Massachusetts Office of the Commissioner of Probations even checks profiles of youth offenders for evidence of probation violations (or plans to violate probation).

Due to current privacy laws (or lack thereof), police can even create a fake profile to gain access to information. While social networking sites say that creating a false profile is against the Terms of Service, if a user voluntarily gives a law enforcement official access to his or her profile, it's the same as allowing any stranger into your house without a search warrant.

Most users probably have nothing to hide, and not all local police departments are even Web-savvy enough to be using social networks in this manner. But you may want to rethink posting pictures of that senior day kegger on your profile. Or accepting that friend request.