A US legal amendment has made it an offence to annoy anyone anonymously over the internet.

President Bush signed the Violence Against Women and Department of Justice Reauthorization Act of 2005, which includes a clause on 'cyber-stalking'.

This amends existing telephone harassment laws and extends them to the internet, providing a maximum two-year jail sentence for anyone using use the web "without disclosing [their] identity and with intent to annoy". 

Civil liberties groups have vowed to fight the legislation in the courts under the First Amendment, claiming that it would make it impossible for whistleblowers to operate without putting themselves at risk.

Clinton Fein, a South African activist who runs Annoy.com, was scathing about the new law.

"It appears that one is guilty of a crime if one were simply to 'utilise' a telecoms device 'with intent to annoy' a person regardless of the content or even in its absence," he said. "A conduct rather than a content crime; perhaps waving a BlackBerry in someone's face."