MessageLabs now has evidence that spammers are tricking ISPs into relaying marketing emails through their own email servers. The tactic makes spam look as if it is coming from the ISP itself, making it difficult to block the messages using blacklists.
Research published today indicates that the proportion of spam coming from networks of virus-infected machines went down from 79% to 59%. At the same time, the number of total spam messages has increased. This, MessageLabs believes, is "hard evidence" that spammers are sending their messages via the ISPs' servers.
Spamhaus says that ISPs can deal with the problem; according to Steve Linford, "They've got to throttle the number of emails coming from ADSL accounts. They are going to have to act quickly to clean incoming viruses. ISPs have so much spam — they are too understaffed to call people up and tell them they have Trojans on their machines."






