Spam offering get-rich-quick schemes has doubled in the past month while traditional spam topics like pornography and phishing are rapidly being phased out, according to new research.

Clearswift's monthly spam index has seen three scams rise particularly quickly: money mules, credit card fraudsters and penny-share promotions.

Money mule spam offers the recipient a cut of the proceeds if they accept a money transfer and then send the money on to an overseas bank account. Such funds are typically moved from an account which has been successfully phished.

The credit card fraudsters look for people to accept delivery of goods that are usually ordered using stolen credit card information and then forward them on to the controller.

This could leave the recipients charged with receiving stolen goods, which can lead to a custodial sentence.

The third scam involves promoting so called 'penny shares', low volume shares that cost a few pence. Because they are so cheap and rarely traded the price can double if only a few people are duped into investing. At this point the spammer sells their shares and brings the price crashing back down.

Pornographic spam, however, plummeted by over half during October, and gambling promotions have all but disappeared.

"The general level of awareness of scams such as phishing has meant that spammers are turning to different tricks to earn a living," said Alyn Hockey, director of research at Clearswift.

"They are motivated by money and if it is not bringing home the bacon, they will try something else."

The traditional 419 scam is also in decline, although Clearswift reported that these mails are now shifting to other developing countries or offering shares in mining projects or charity funds.