In between the porn, the hilarious solicitations from supposedly willing Russian chicks and ads touting everything from Viagra to organ enlargements, there's been a rush of spam mails telling the world about "hot stocks" that are set to "skyrocket".

The spammers' plan is mind-numbingly simple: inflate the price of what are usually penny dreadful stocks and create a monster spike. Then dump the shares and make big profits.

But how successful are the spammers? Very, according to a new study, which is worrying news indeed.

The study by two German computer scientists found that the spam waves from November 2004 to February 2006 did send the stock price up sharply, at least in the short term. So some were reading the emails, and then rushing out to buy the recommended cheap shares, sending the stock up by as much as 13 per cent. Sad but true.

More detail on the study in this piece in The Economist.

Professor Stephen Bainbridge points out in his blog that this sort of scam would have limited impact in an efficient market. His advice: delete the spam.

Good point. Trouble is the spammers are becoming more sophisticated. I've noticed the topics in the subject field are becoming more deceptive, although when you get a few hundred a day - and as a business journalist, most of the ones I get are touting stocks I've never heard of but which I'm always told are about to "explode" - you know which ones to delete without even reading.

Here's what I do. When ever I have to fill in customer information on application forms, I always make sure I say that I am 75 years old and I am in the lowest possible income bracket.

OK, so I lie. But with that sort of information, they don't even want to know me!