Pump-and-dump spam domains have gone quiet since the closure of a major botnet operation earlier this month. The finding, by Alex Shipp of MessageLabs, suggests that a botnet (a network of compromised machines controlled by hackers) thought to be associated mainly with adware distribution was also used to distribute junk mail on a massive scale.

Spammers register pump-and-dump spam domains for use in spam runs. These domains are commonly discarded after a few days. The tactic is commonplace but the the arrest of alleged botmaster Jeanson James Ancheta, 20, of Downey, California, on 3 November has been accompanied by a radical shift in the landscape.

"Up to recently, the graphs were all fairly smooth, with the stats showing that 12 days was about the maximum lifetime for this type of domain, while 30 per cent only lasted a day or under, and 10 per cent only lasted three hours or under," Shipp said. "This kind of activity just disappeared completely from the radar on 2 November."

Shipp reckons that the changes in pump-and-dump domains (which are mostly still live though inactive) are "too big a coincidence" to be explained by pure chance. ®