An analysis of so-called 'pump and dump' stock spam has shown that online criminals are getting much more sophisticated at manipulating the stock market for financial game.

The analysis, carried out by the National Cyber-Forensics and Training Alliance (NCFTA) and Secure Computing, has shown that far from spam about stocks raising the share price, in fact the price usually drops. Instead the criminals buy up the available shares before the spam campaign and simply sell to new buyers, for almost pure profit.

People who invest in such stocks on the expectation that the price will rise in the short term are likely to take a bath, according to Dimitri Alperovitch, principle research scientist for Secure Computing.

"Follow the spam trading is a very bad idea," he said.

"The stocks seldom rise much and the spammer can always underbid you since they already bought the shares for almost nothing."

But a new and more devious method is now in use by the criminals. This involves stealing stock trading account login details and profiting from crime more indirectly, thus making themselves much harder to catch.

These stock manipulation scams typically involve a criminal who sets up a stock tip messaging service. This sends out stock tips to investors, both legitimate and illegitimate. The service can be very highly priced, as much as $1,000 per tip, because the criminal uses stolen share trading accounts to make sure the predictions are accurate.

Secure Computing's Alperovitch used a real world example of a stock that was forecast to rise from $3.45 to $3.90 over the space of one hour. Stolen trading accounts made sure the correct price was reached, but the authorities were able to catch the two men involved.

In the past stock spam trading was confined mainly to penny stock companies that are easy to manipulate, but increasingly the scammers are using NASDAQ, AMEX and the Frankfurt stock exchange.