McAfee is warning that the number of spammers using the out of office or "vacation" functions of web-based email services to send spam is in the rise. These auto-responders are configured to send spam rather than a real "out of office" message.

"In recent weeks we have seen an increasing number of spam apparently sent by legitimate Web-based e-mail systems," said Jeremy Gilliat, an Aylesbury, UK-based anti-spam engineer at McAfee. "Interestingly we see spam from a number of accounts being abused in this way. I suspect the spammer has a program that automatically creates accounts and sets the responder text, all with no manual work required. This gives the spammer the capability to have lots of Web-mail accounts, all used to spam lots of people."

This is yet another way spammers have found to get around spam filters. Naturally, McAfee claims its filters are not so easily fooled. However, there is no way to tell that that spam is an auto-response except by carefully examining the headers. The current product being advertised this way is an adult website, but with the technique becoming more and more popular, expect to see all the usual pharmacy, mortgage and stock spam joining the auto-responder parade.