Think twice before wiring money to help a Facebook friend who claims to be in trouble in a foreign country.

Marking the commencement of National Cybersecurity Awareness Month, the Federal Bureau of Investigation (FBI) on Thursday warned that there's been an increase in hijacked social networking accounts and that cybercriminals are using these accounts to defraud victims' friends.

Since 2006, there have been 3,200 reports of account hijackings, according to the Internet Crime Complaint Center (IC3).

Such scams often begin with spam messages.

"When opened, the spam allows the cyber intruders to steal passwords for any account on the computer, including social networking sites," the FBI said. "The thieves then change the user's passwords and eventually send out distress messages claiming they are in some sort of legal or medical peril and requesting money from their social networking contacts."

Facebook's security blog includes a transcript posted in August of a chat conversation in which this very scam is played out.

"Pretending to be Derek's friend Jill, the scammer tells Derek that she was mugged at gunpoint in London, and that she needs him to wire her $890 immediately," Facebook explains. "Derek becomes more and more suspicious as the conversation progresses and ultimately realizes that the person he's talking to isn't his friend, and that the story he's being told is a lie."

Another common scam, the FBI said, involves phishing spam that presents a fake notice about some issue requiring attention, such as a terms of service violation, account expiration, or unexplained account activity. Messages of this sort often seek to prompt recipients to click on a link that leads to a malicious site and to provide personal information or account details.

The reason that cybercriminals seek to abuse social networking accounts is that messages from friends have an appearance of legitimacy.

As if to underscore the FBI's concern, Roger Thompson, chief of research at AVG Technologies, reported in a blog post on Thursday that his company had detected a series of identical Facebook profiles, differentiated only by profile names, set up to distribute fake anti-virus software through a link purporting to be a home video.

The FBI advises: that users check their privacy settings on social sites to make sure they're not exposing too much information; being selective about friends on social sites; disabling unused sharing options; being careful about links posted to social sites; and reviewing the security settings and procedures at social sites.

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