Pharmacy-touting spammers can turn a decent return on response rates as low as one in 12 million, far lower than previously thought.
So say security researchers at the University of California, San Diego and UC Berkeley, who infiltrated the control system of the Storm botnet to research the economics of spam.
At the peak of its activity in September last year, yhe Storm network of compromised PCs spewed out up to one in five junk mail messages.
Over 26 days this spring, the Storm botnet generated 350 million junk mail messages promoting the researchers' dummy pharmacy sites. The virtual storefronts established by the researchers only mimicked the penis pill pushing sites typically spamvertised using the Storm botnet.
The dummy sites worked up until the point of purchase. They returned a site error message after would-be customers tried to pay for goods in their shopping cart but before prompting for credit card details or shipping information. In this way the researchers avoided the collection of any personal data.
The huge volume of junk mail the researchers redirected generated just 28 attempted sales - all but one for male enhancements products - with an average "purchase" of just under $100 or $2,731 in total. The researchers reckon one in four of the emails they subverted made it past spam filters and conclude that this level of return only makes sense if the unknown bot herders have set themselves up as affiliates of pharmacy sites.
Renting a botnet, or hiring a third-party to send spam, with these low levels of return would not make economic sense, the Californian academics conclude.
All above board
At first sight it might appear that the researchers were sending spam to study spam. But the set-up is more complicated than that and above board, according to security experts we asked to comment of the ethical implications of the exercise.
"The researchers didn't send any spam themselves, but instead subverted part of the Storm botnet into sending a spam template which pointed to their own innocuous website rather than the one that the real spammers wanted people to arrive at," explained Graham Cluley, senior technology consultant at net security firm Sophos.
"As such - no extra spam was sent, but more of the spam which was sent was non-dangerous," he added.
The Californian academics reckon they misdirected the activity of about 1.5 per cent of the compromised worker bots than made up the zombie drones in the Storm worm botnet. Based on this estimate, and their own findings during the experiment on sales conversion, the researchers estimate the Storm worm generated $7,000 or $9,500 in pharmacy sales a day during the time of the experiment.
Separately ,the researchers looked at the percentage of users who clicked on the type of link that normally leads to websites harboring the Trojan downloader code that turns vulnerable Windows PCs into Storm worm zombie drones.
They hijacked Storm worm email lures and discovered one in ten people who received the email clicked onto what would normally have been dodgy domains. Based on circumventing 120 million malware-propagating messages, that it might be possible to infect between 3,500 to 8,000 drones a year, the researchers say.
More details can be found in a paper here (PDF). ®