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 "from" 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's email account.

"Zombie" 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 (New Scientist, 26 March 2005, p 25).

Hackers generally use bots to gain access to credit card numbers and passwords. With only slight ...