So-called spam king Alan Ralsky has been sentenced to over four years in prison for his involvement in a pump-and-dump stock fraud.

Ralsky was sentenced to 51 months in prison, with five years' supervised release on completion of his jail term, and has been ordered to pay a fine of $250,000 (£150,000). His son-in-law Scott Bradley received a 40-month sentence.

"With today's sentence of the self-proclaimed 'Godfather of Spam', Alan Ralsky, and three others who played central roles in a complicated stock spam pump-and-dump scheme, the Court has made it clear that advancing fraud through abuse of the internet will lead to several years in prison," said Terrence Berg, US attorney for the eastern district of Michigan.

"I commend the FBI, the Postal Inspection Service and the IRS Criminal Investigative Division for their determined and careful investigation in this case which led to today's result."

Ralsky was found guilty of sending millions of spam emails about trades in penny stocks, designed to entice people to invest, thus driving up the price and enabling the owners of the stock to profit.

The authorities said that Ralsky had made $3m (£1.8m) in the scam after trading in Chinese stocks via US exchanges.

Two other co-conspirators, How Wai John Hui from Hong Kong and John S. Bown from California, were sentenced to 51 and 32 months in prison respectively for their parts in the scam.

"Through this conspiracy Ralsky and the others were able to manipulate the stock market and maximise their profit. They flooded our email boxes with unwanted spam, and attempted to use a botnet to hijack our computers to assist them in the scheme," said Andrew G. Arena, special agent in charge at the FBI.

"Cyber crime investigations are a top priority of the FBI and we will continue to aggressively investigate those individuals who use and hide behind computers to commit various crimes."