FACEBOOK users, beware: downloading applications from the online social networking website may open your computer to unwanted guests.

United States based Internet security vendor Fortinet discovered that an application, called Secret Crush, which invites people to find out who among their friends has a secret crush on them, is malicious.

Users tempted to discover more have to invite at least five other Facebook users to install the application before their mystery admirer is revealed.

However, no secret crush is ever revealed. Instead, users are directed to an external website which invites Facebook users to download potentially unwanted applications such as MyWebSearch that will display pop-up advertising.

According to IT security company Sophos, which has headquarters in Britain and the US, more than 50,000 people were using Secret Crush daily.

Yesterday, IT website CNET News.com reported that Facebook has banned the application, although online media company Zango, which has been associated with adwares, claimed that the application never disappeared - it had just changed its name to My Admirer.

This is not the first time Facebook has faced security loopholes, since founder Mark Zuckerberg opened up the site last year for third-party developers to create new applications to increase content.

Wired magazine, an authority in technology news, reported earlier this month in its website that hackers originating from a China domain have been harvesting the information such as users login details and passwords.

IT security company Sophos, which has headquarters in Britain and the US issued a statement yesterday to advise Facebook users to be careful.

Mr Graham Cluley, a senior technology consultant for Sophos, said: "These third-party widgets are not written by Facebook, and can mean that you are carelessly sharing your personal information with strangers or risking your computer's security."

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