The US Air Force became the latest victim of a series of hacking attacks on US government computers after its home page was tampered with and covered in obscenities and bizarre allegations of alien landings.

The site, maintained by the US Defense Technical Information Center, was altered to include dripping blood, pornography, and links to X Files-style exposes of a government cover-up of alien landings.

When the incursion was detected, air force authorities ordered that access to 80 other military Web sites should be suspended. A representative later insisted that the hackers only had access to one Defense Department PC.

But a man who claims to have been involved with the hacking contacted the US media to say the hackers had access to the entire air force email system, including classified documents. 'Their security on government systems is simply pathetic,' he said. 'A foreign government could go through that security in a few minutes.'

Captain Terry Bowman, chief of the air force public affairs technology integration team, said in a statement: 'We continually review our security procedures to maintain the integrity of information on our site.'

In October, hackers rewrote the CIA home page, and the Justice Department's page was tampered with in August. The hacked air force home page was altered to display a logo reading 'Welcome To The Truth' with text underneath that went on: 'You can learn all about government corruption here. Learn the secrets that they don't want you to know.'