Facebook users are at risk from malicious hackers targeting the site, online security experts warned.

Account holders have been hit by several different hacking attempts in the last week, as thieves try to capitalize on the trust users place in the service.

Rik Ferguson, senior security adviser at Tokyo-based Trend Micro, said that Facebook, which has more than 174 million active users worldwide, had been hit by four separate "rogue applications" and a virus targeted at users of the site.

Hackers are now seeking to take advantage of the popularity of social networks such as Facebook and MySpace to get users to divulge personal details, he added.

Facebook allows people to develop and write software applications to run on the site, but they do not need to be approved by Facebook before they are made available for people to download.

Ferguson called for Facebook to review its security processes.

"I think that it is time Facebook had a review of its application vetting policy. It launched a service in November last year where people can pay to get their applications approved, but it is voluntary," he said.

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