BOGUS sales pitches hawking cosmetic enhancements and get-rich-quick schemes might no longer be confined to bulk emails sent by spammers. Annoying advertisements and malicious attachments could start appearing within the text of emails from friends, family and colleagues.
Although spammers frequently forge the 鈥渇rom鈥� address on their emails to make them appear to have come from a bona fide source, they still have to create the email messages themselves. The majority are blocked by filters or automatically deleted by the recipient鈥檚 email account.
鈥淶ombie鈥� computers could change all this, according to Morton Swimmer, an anti-spam researcher at IBM Research in Zurich, Switzerland. A computer becomes a so-called zombie when hackers gain control of it by using a virus to deposit a piece of malicious code, or bot (麻豆传媒, 26 March 2005, p 25).
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Hackers generally use bots to gain access to credit card numbers and passwords. With only slight modifications, they could use them instead to monitor the inbox of the computer鈥檚 owner and fill their outgoing emails with spam, Swimmer says. 鈥淭he spam is being piggy-backed on a legitimate piece of email.鈥� The bot could add spam to the beginning or end of a message, replace web links inside emails with the spammer鈥檚 own links, or add a virus-laden attachment.
Existing spam filters are not programmed to cope with emails containing a mixture of spam and legitimate content. 鈥淚t is up in the air what a spam filter would think,鈥� says John Graham-Cumming, an independent email security consultant based in Toulouse, France. But whether the filters block or accept the 鈥減arasitic鈥� spam, email users will suffer, as they will either be forced to receive spam mail or lose legitimate messages.
Thankfully, no parasitic spam has yet been detected, but Swimmer says it poses a serious risk. According to security firm Ciphertrust in Alpharetta, Georgia, there are around a million zombie computers in the US at the moment, and approximately the same number in China and Europe. Last week SurfControl of Scotts Valley, California, warned that hackers had built a fake Google Tool Bar website to trick people into downloading code to turn their computers into zombies.
Swimmer says bots running on existing zombies could be modified remotely to turn them into parasitic spam zombies. He suggests that filters could be redesigned to detect 鈥渟pammy regions鈥� of emails and carve them out, or to monitor the correspondence between people and flag unusual patterns in the content of emails.
His team will warn about the risks of parasitic spam at the Conference on Email and Anti-Spam in Mountain View, California, this week.
