Research from security firm Clearswift uncovered a large number of fake financial tips, where spammers coaxed recipients in the financial sector into purchasing particular stocks.
"It is hard to believe that spammers can influence stock market prices," said Alyn Hockey, director of research Clearswift. "But they wouldn't be sending these emails unless there was something it for them. I would advise people to be extremely dubious of any claims made in emails unless they come from a trusted source."
While pharmaceutical messages dominated Clearswift's Spam Index with 57 per cent of all spam, financial spam rose from 10.8 per cent to 26 per cent last month.
Clearswift added that the proliferation of the emails suggested new revenues for spammers, and demonstrated how vulnerable people are to the offer of quick financial gain.
The figures were taken from thousands of unsolicited emails received by the firm and spam submissions forwarded by its 20 million global users.