The firm said hundreds of thousands of users have been hit with the fake ads, which appear to show a link to a video called "distracting beach babes".
The company has said the ad will take users to an app that tells them they do not have the right video player installed. Instead of the real video player, users will download adware designed to spam their computer.
"This is a typical online 'bait and switch'," Paul Ducklin, head of technology at Sophos Asia Pacific, said in a statement.
"The bait is the movie; the switch is that you don't get to see a movie - you are tricked into using a bogus Facebook application and into installing unwanted software instead. Other bait-and-switches seen on Facebook include the offer of a free iPad; if you bite, the bait is switched and you are asked to sign up for an expensive SMS service first. Of course, there never was a free iPad."
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