Rhodri Marsden: Cyberclinic

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

The number of e-mails I've received recently from people complaining about spam has been outnumbered only by spam itself. Some monitoring services have detected a 450 per cent increase in the past eight weeks.

Nigel Allam's complaint is typical: "My ISP has spam filtering, as does my e-mail 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" - are becoming useless; spammers either suffix messages with passages of text from novels or news stories to make them read like normal e-mails, or they place the message within a graphic file, rendering it invisible to text searches.

Scott Petry, from e-mail experts Postini, says that "images make it hard for conventional blocking technologies to detect spam". Graham Cluney, from net security firm Sophos, adds: "These images are randomised 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. This is mainly because many spammers no longer rely on their own servers to send e-mails, 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 choose your domain name as the false source for their spamming activities. "I'm receiving hundreds of bounceback messages, as if my e-mail address is being used to send out spam," writes Richie Houston. This situation can often be cured by asking your ISP to turn off the "catch all" facility that forwards all messages sent to your domain; if your e-mail address is mail@nospam.co.uk, you might receive messages sent, for example, to gf8djp7@nospam.co.uk. Many ISPs turn this off by default to protect customers, and with 80 per cent of all e-mail now consisting of spam, we need all the help we can get.

Diagnosis required

Next week's question comes from Iain Hillier:

"I've been reading about the online virtual-reality game Second Life, and I'm unsure as to whether it's a thrilling social development, or a cynical and slightly sinister scheme for making money. Which is it?" Any comments, and new questions for the Cyberclinic, should be emailed to cyberclinic@independent.co.uk.