So-called pump-and-dump spam scams happen when spammers send out massive amounts unsolicited e-mail with false or misleading statements to hype stocks, which are then "dumped" on the public at inflated prices for a profit.

Security researchers at Sophos warned recently they have detected a widespread pump-and-dump scam that has caused spam levels to soar by almost a third. The message contains a PDF file which urges the recipient to buy shares in a company called Prime Time Group Inc. touting quick money to be made on stock.

"The share price in this company has rocketed as a result of bogus news being blasted to internet users worldwide. In an attempt to get past anti-spam products, criminals are now regularly using PDF files to carry their slick enticements for potential investors," said Graham Cluley, senior technology consultant for Sophos.
Pump-and-dump stock campaigns currently accounts for approximately 25 percent of the world's spam, according to Sophos, and are often propagated by thousands of virus-infected home computers. More details on the latest pump-and-dump campaign can be found at Sophos' website.