That guy you just friended on Facebook might be a second-story expert looking to liberate your plasma television while you’re on the vacation you just wrote about on your wall. And it’s possible some of your followers on twitter are following you, not because they care what you had for lunch, but for larcenous reasons.

Social networking is potentially more dangerous than you might think, according to a report, The Digital Criminal, released by U.K.-based Legal & General, a financial and insurance organization.

The study found that 38 percent of users of sites such as Facebook and Twitter post status updates detailing vacation plans and more than a third of socnet users post updates that say when they are going to be away from home. Mash those numbers up with the finding that a high percentage of users are willing to be “friends” online with people they don’t know, and you’re looking at a potentially serious security threat to your home and stuff.

More disturbing still, the report found that nearly a quarter of social media users discussed their vacation plans publicly “wall-to-wall,” or outside the privacy of their own page, and 17 percent reported seeing people’s residential addresses posted on publicly accessible pages.

Legal & General’s research uncovered a widespread casualness among socnet users toward meeting strangers online: 79 percent think social media are a great way to find people they met on vacation, three-quarters feel they are a good way to meet friends of friends, and 47 percent use socnet sites to meet new people based only on the person’s photo.

Legal & General conducted an experiment to see how many U.K. social media users would accept a “friend” invitation from a complete stranger. Of 100 “friend” or “follow” requests issued to randomly selected strangers, 13 percent were accepted on Facebook and 92 percent on Twitter — without any checks. As a result, it’s possible that a complete stranger with evil intent could learn about a person’s interests, location and movements in and out of their home.

Reformed burglar Michael Fraser, star of the BBC’s “Beat The Burglar” series, consulted with Legal & General on the study:

“In just one week, a professional burglar, or a team, can use social networking sites to harvest dozens of potential targets,” said Fraser. “New users of Facebook, for example, will be a key target, as they are keen to build up their number of ‘friends’ or ‘followers’. People with specific interests are also easy targets. Pet owners are a good example — their home security is often not of a sufficiently high level, as they rely on their dog for security, have cat flaps that weaken a back door, or leave their alarms turned off.

“For a burglar, this kind of information is power — it breeds confidence. Once you start seeing people’s holiday movements, for example, you know when they are leaving their home unattended. By giving away this information, people are making the burglar’s job a lot easier.”

Other study findings include:

  • Nearly half of respondents are not worried about the security or privacy of social networking sites.
  • Of all social networking sites, Facebook creates the most concern, with 46 percent of respondents believing there are some security and privacy risks.
  • The younger you are, the more likely you are to give information away concerning your whereabouts, with 64 percent of 16- to 24-year-olds sharing their vacation plans, which could be a cause for concern for parents.
  • 34 percent of respondents have seen someone’s phone number posted on their social networking profile.
  • Nearly one in 10 respondents have included their phone number and 5 percent have included their address in the personal information section of social networking sites that are visible to friends.
  • Some people share cell phone numbers and e-mail addresses directly with strangers — 6 percent have written their phone number and 3 percent have written their address “wall-to-wall” or on pages open to those who are not accepted contacts.
  • Men are more blasé about personal information — 13 percent have included their cell number on their profile compared with just 7 percent of women, and 9 percent of men have included their address, compared with just 4 percent of women.
  • 70 percent of users think that social media sites are a great place to share photos of new purchases and presents.