An American state has upped the ante in the war against spammers by introducing five-year jail sentences for persistent offenders.

Virginia has passed a law that it hopes will go some way to stamping out those ubiquitous emails that promise money for nothing, generic Viagra, penis enlargement devices and other false claims such as non-existent competition wins or prizes.

It will apply to businesses or individuals who send more than 10,000 messages. Other states have claimed success for their anti-spam legislation and Virginia hopes its tough stance will stem the flow.

An estimated 45 per cent of all emails are spam. Of these, 66 per cent are fraudulent in some way.

The majority of spam originates in the US and Far East. As well as state legislation, US federal laws are in the pipeline which would fine and/or imprison spammers who fail to label their messages to show the content or offer an opt-out option.

The Federal Trade Commission's (FTC) Bureau of Consumer Protection admitted that enforcing these laws internationally could prove problematic, but that current agreements with other countries, like the FTC's joint venture with the UK's Office of Fair Trading, have enjoyed some success.