Some of the spam contains "run-of-the mill" Viagra-type messages, but some of it is more dangerous, Facebook spokesman Barry Schnitt said Thursday. "Some of it points to a site where users are hit with drive-by downloads of adware," he said in an e-mail message. " We’ve started blocking all of this spam this morning, have been deleting it, and resetting the passwords of accounts that sent it."

One of those sites, mygener(dot)im, (do not visit this Web site; it will attack your computer) is loaded with attack code that is used to install malicious programs, said Paul Ferguson, a researcher with antivirus vendor Trend Micro. The site is hosted at a Latvian data center that has been associated with other cybercriminal activity, he said. "My gut feeling is that it's the same criminal operation that was involved with the Russian Business Network," he said, alluding to an organized gang of cybercriminals based in Russia.

Attackers have also used the fbaction(dot)net and fbstarter(dot)com domains in their scams, Schnitt said.

Facebook's 200 million users were hit last week with several rounds of phishing attacks, which tried to trick victims into visiting phoney sites designed to look like Facebook login pages. Users who think they may have fallen victim to one of these attacks are urged to reset their account passwords.

Facebook is disabling accounts that it links to the recent spam attacks, but the company won't say how many users have been affected, because that would let the bad guys know how effective its security measures have been.