Online fraudsters are ramping up spam attacks through emails designed to look like automated responses to undelivered messages, according to recent figures from PandaLabs.

The cloud security firm saw a 2,000 per cent increase in the number of malware laden non-delivery report (NDR) messages in August, compared to the average monthly number in the first six months of 2009.

Legitimate NDRs are automated messages sent to someone by a mail server when it cannot deliver an email to the intended recipient. This is usually because the email address has been entered incorrectly, the account has been deleted or the recipient's inbox is full.

Around one in five global spam emails detected by PandaLabs is using this technique, making it one of the most pervasive forms of spam currently in use.

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