Hackers succeeded in stealing information from the US Department of Transportation and several US companies by enticing employees to click on fake job advertisements, a computer security firm has revealed.

Victims of the scam included consulting firm Booz Allen, IT services company Unisys, computer-maker Hewlett-Packard, and satellite network provider Hughes Network Systems, says British Internet security provider Prevx.

Only Unisys has confirmed it detected the presence of viruses on two PCs, adding that no information had been leaked.

Prevx has taken the unusual and commercially dangerous step of exposing victims of the attack in a bid to highlight the major vulnerabilities of government IT systems, said the company's CEO Mel Morris.

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