"The Trojan is able to order proxies to send spam upstream to the ISP," said Steve Linford, director of SpamHaus.
Linford believes that this Trojan was written by the same people who write spamming software.
Reports suggest that ISPs in the US have already been hit. "We've seen a surge in spam coming from major ISPs. Now all of the ISPs are having large amounts of spam going out from their mail servers," said Linford.