Facebook has announced that hackers have targeted it in a "sophisticated attack" but that it has found no evidence of user data being compromised.

The social networking site said it discovered the breach last month and that the attack occurred when a handful of employees visited a developer's compromised website, which led to malware being installed on their laptops.

The company said that it has fixed the infected machines, informed the authorities and initiated an investigation.

It added that it was not the only company targeted in the attacks but was one of the first to discover it, and that its security teams are working with those at other companies to find out all it can about the attack.

"As one of the first companies to discover this malware, we immediately took steps to start sharing details about the infiltration with the other companies and entities that were affected," Facebook added in a statement posted on its security blog.

"We plan to continue collaborating on this incident through an informal working group and other means."

Under Facebook's White Hat programme, anyone who finds a way of breaching the site's networks and owns up can earn rewards worth thousands of dollars. As well as money, the site promises not to land them in trouble with the police if they have complied with the programme's golden rules.

One British hacker has earned more than £1,500 from Facebook, and the most prolific White Hat contributors have been given their own Facebook "bug bounty" credit cards.