Many people I know have had a massive increase in junk email recently, and it seems to be getting better at passing the filters. Why?

The number of emails I’ve received recently from people complaining about spam have been outnumbered only by spam emails themselves. Some monitoring services have detected a 450% increase in the last eight weeks, while ISPs in New Zealand recently reported a tenfold surge in one week alone, crippling their networks. Nigel Allam’s complaint is typical: “My ISP has spam filtering, as does my email program, but things have got much worse in the last month or so.” The old methods used to filter out spam – scanning for keywords such as “viagra”, “erection”, or “slimming” and their variants – are becoming useless; spammers either suffix messages with passages of text from novels or news stories to make them read like normal emails, or they place the message within a graphic file, rendering it invisible to text searches. Scott Petry from email experts Postini notes that “images make it hard for conventional blocking technologies to detect spam,” while Graham Cluney from net security firm Sophos adds: “These images are randomized in terms of size and content, and until anti-spam products are updated to deal with this you’ll inevitably get more junk mail.”

So on one hand the filters are failing us, but there has also been a huge increase in the amount of unwanted mail swilling about. This is mainly because many spammers no longer rely on their own servers to send emails, but instead use a large network of PCs that have been compromised by a virus – otherwise known as a botnet – which has a far greater capacity to pump them out. It’s possible, then, that your machine could be controlled remotely to send spam, but a far more common nuisance is when spammers randomly choose your domain name as the false source for their spamming activities. “I’m receiving hundreds of bounceback messages, as if my email address is being used to send out spam,” writes Richie Houston, “but I’m certain that I don’t have a virus.” Richie’s probably right; many correspondents have received furious emails requesting that they cease spamming, and few of those people have stockpiles of impotence drugs or Rolex watches in their garages. This particular situation can often be cured by asking your ISP to turn off the “catch all” facility that forwards you all messages sent to your domain; if your email address is mail@nospam.co.uk, you might be receiving messages sent, for example, to gf8djp7@nospam.co.uk. Many ISPs turn this off by default to protect their customers, and with 80% of all email now consisting of spam, we certainly need all the help we can get.