Non-delivery report spam 'up 2000 per cent'

August saw a 2000 per cent increase in the amount of different non-delivery report - NDR - spam messages in circulation since Q1-Q2/09, security specialist PandaLabs has reported.

 Some such spam now accounts for 20 per cent of global spam monitored by the company. These messages are usually legitimate, but this mail server function is being exploited by spammers to distribute spam, using the sender’s real name

The spam content is usually sent as an attachment to the fake non-delivery notice. Although in most cases users have not sent the supposedly undelivered email, they still become curious, and open it, says Luis Corrons, PandaLabs technical director.

“There is no consensus on whether NDRs are a technique to evade anti-spam filters or a collateral effect of dictionary attacks - either way, this technique is now among the most widely-used,” Corrons explains. “These waves of spam are usually generated through botnets - infected PCs controlled by attackers to launch spam, and so forth. Since most NDRs are legitimate emails and, part of the mail server functionality, many traditional anti-spam techniques did not detect or block them up until now.”

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