Affected users receive a notification that someone has commented on one of their posts, but clicking on the hyperlink in the notification leads to a malicious site hosted on the fucabook.com domain, according to Trend Micro senior security advisor Rik Ferguson.
The malicious site then pulls up the real Facebook log-in page to prompt users to enter their details again.
The notifications appear to come from a dubious sounding app called 'sex sex sex and more sex!!!' which has over 287,000 users signed up already, said Ferguson. He warned users to always check the URL of a site in the browser bar before entering sensitive information.
"Also check the true destination of a link before clicking it by hovering your mouse pointer over it. If it looks suspicious, don't click it," he wrote in a blog post. "Also, if you're a Facebook user, now would be a good time to review your privacy settings and clear out any applications you no longer use."