Facebook has begun warning its users to avoid bogus links and fan pages that offer free gift cards because they are scams aimed at stealing user identities.

Facebook Security says it tries to remove these links and pages as quickly as it can find them.

"Watch out for suspicious offers for free gift cards," the Web site warns. "We've been removing groups and Pages that promise free gift cards, but instead trick people into entering information or spamming their friends. If you come across one, report it to us immediately."

The schemes usually work this way: a "friend" writes on your wall telling you about the gift card offer. Usually the alleged gift cards are for well-known retailers like Best Buy or Ikea. The user is then directed to a third-party Web site where they are told to fill in all sorts of personal information -- sometimes even a debit or credit card number.

Afterward the victim is directed to the actual site of the retailer, a move presumably to lull the victim into thinking the offer is legitimate. However, by that time the scammer has all the information he needs to do some real damage.

PC World reports that a bogus $1000 Ikea gift card offer drew more than 70,000 Facebook users to a scam page before Facebook Security discovered it and took it down. Victims are usually alerted through spam, but also by legitimate "friends" who have been taken in by the scheme in a story today.

When criminals gain access to a Facebook account, they usually post spammy comments on friends' Walls, or send spammy messages through Inbox or Chat," the Web site said. "Don't click on strange links in posts or messages, even if they're from friends."

If it seems weird for an old friend to write on your Wall or send you a message, Facebook cautions, it's possible that the person's account has been taken over by a spammer. As always, be particularly cautious of posts or messages that contain misspellings or use bad grammar.