Alternative spelling

Perhaps the most common method for spammers to bypass filtering software is by spelling words incorrectly. Two common products sold by spammers could be spelt 'V1agra' and 'M0rtg4ge', and go unrecognised as the commonly blacklisted words, while remaining readable.

Acting as a trusted source

A recent virus distributed across the Internet purported to be from the @msn.com domain. While many filters should have detected the virus and quarantined it accordingly, the message could have been effective spam. By including domains, IP addresses or phrases from commonly trusted online sources such as vendors or Internet registries, spammers take advantage of filter or individual user settings that may accept mail containing the addresses of those trusted sources.

URL encoding

This HTML trick was used to target customers of Australian banks this year. A spammer can send e-mail that does not push its message and is rightly accepted by filters. Instead, the spammer's message, or Web site, is encoded in a link which displays in the e-mail as a commonly accepted wording or address; for example, 'click here' or 'ANZ Bank online'. The URL of the spammer's Web site will often determine the difficulty of filtering this sort of spam.