The number of hijacked social networking accounts is on the rise, according to a warning issued by the FBI this week. (For free advice on how to protect yourself online, see our Online Security Guide.)

The warning addresses one of the more popular online scams, perpetrated on sites like Facebook and Myspace: Criminals plant malicious software on a victim’s computer, hijack their social networking account, then use the account to send emergency distress messages, for example claiming they are in legal or medical peril, requesting money from their social network contacts.

The FBI’s announcement also describes several other online scams, such as spamming to promote phishing sites and distributing malicious software via social-networking “applications.”

One of the best ways to protect yourself against malicious software is to use an effective security software suite. Our Ratings of security software (available to subscribers) provide recommendations on which products offer the best protection.

If you’re looking for a free antivirus, be aware that Microsoft has just released its own called Microsoft Security Essentials. We haven’t tested it yet; we will be posting more details on this product in this blog very shortly.

For the rest of October, which is National Cyber Security Awareness Month, we’ll continue to post the latest news and advice about online security. —Jeff Fox