An IT security firm has warned computer users to be on their guard against so-called 'Letters from Nigeria' as rumours of Chelsea Clinton's new boyfriend and his convicted father have been published in the press.

American tabloids have reported that Bill and Hillary Clinton's daughter is secretly dating young investment banker Marc Mezvinsky.

The relationship has thrown into the spotlight the curious story of Mezvinsky's father, former Iowa congressman Ed Mezvinsky, who is currently serving a prison sentence for internet fraud.

Mezvinsky, who was at one time an ambassador to a United Nations commission, turned his back on politics in the 1990s and fell victim to a number of 'advanced fee fraud' schemes (also known as '419 scams') that promised great wealth.

To continue participating in the schemes, Mezvinsky used money stolen from others and was convicted in 2003 on 31 counts of fraud.

It is estimated that $10.4m was defrauded from banks and individuals in total. Mezvinsky is not expected to be released until November 2008.

"The story of the rise and fall of Ed Mezvinsky acts as a useful warning that anyone can be caught off guard and fall for a 'Letter from Nigeria'," said Graham Cluley, senior technology consultant at Sophos.

"These emails promise riches, but are actually con tricks designed to leave you out of pocket. Everyone should be suspicious about unsolicited emails."

419 scams are named after the relevant section of the Nigerian penal code where many of the scams originated and are unsolicited emails where the author offers a large amount of money.

Once a victim has been drawn in, requests are made from the fraudster for private information which may lead to requests for money, stolen identities and financial theft.