There’s a new password-swiping virus spreading on Facebook, and once again the malware preys on the social trust accrued by the network.

Over 800,000 people have already been affected by the virus, which looks like a video sent by a friend. Once someone clicks on it, they are routed to a website that tells them they need to download a plug-in to watch the video.

And if they download the plug-in is when trouble starts. The download gives the malware creators access to a user’s password, often for email as well as Facebook and Twitter. This gives the attacker the ability to pretend to be their victim, potentially wringing more personal information out of their accounts. This is how the virus spreads; since the attackers have access to the infected accounts, they use those handles to reach out to other victims, spreading the video.

Carlo de Micheli, one of the researchers, told the New York Times that instances of the attacks were growing rapidly, with 40,000 new cases an hour.

Google responded by disabling browser extensions that allowed the attack, which may seriously impede future growth. But while the attackers were primarily using the Google Chrome browser, De Michelli said that the attackers were adapting their malware program to get around defensive measures, and that they had already adapted it for Mozilla Firefox.

This latest attack is troubling because it shows a substantially more sophisticated understanding of how to take advantage of Facebook to spread spam than other attacks. Because this type of attack, where the user is prompted to download a plug-in, is not very well-known, even users who are generally savvy about viruses can get duped. This isn’t your typical weight loss link popping up, supposedly recommended by your friend. This looks like it’s a message directly to you.

As malware attackers continue to innovate ways to get at your personal information, it’s important to assume that anything sent to you may be spam. Look for signs that an email or Facebook message is actually addressed to you – for instance, if you got this newest virus sent to you, it wouldn’t be a personalized message, but just a link from your friend. Do your friends often send you links without any comments? If so, tell them next time to put a little personal remark next to the link so you know it’s not a virus.