If you ever wonder who’s behind the deluge of spam that hits your computer each day, they may be a lot closer to home than you first imagined.

As the BBC reports, a team of Dutch researchers investigating ways to curtail the hijacking of domestic computers for criminal use, found that more than one million UK households’ PCs are linked to criminal networks known as ‘botnets’, which are groups of Internet-connected computers that have been compromised by a third party and put to malicious use.

With around 6% of the UK’s 19m Internet households thought to be part of a botnet, this helps criminals spread spam around the Web more effectively, whilst it can also be used to attack websites and even garner bank details from the unsuspecting public.

The data was gathered from a number of different sources, though most emanated from what is known as ‘spam traps’, which are fake email addresses set up for the sole purpose of receiving junk mail. It’s thought that more than 90% of spam is sent through botnets, and it’s the Internet addresses on these botnets which are a good indicator of where the so-called ‘drone’ machines are located.

The researchers then used the IP addresses of the machines that were sending the spam, and traced each one to an Internet Service Provider (ISP). And feeding into this was data about the Conficker botnet, which is thought to be one of the biggest examples of such a network, and incident reports from a computer security company called DShield.

The UK figure is placed at number 19 in the top 20 nations with the biggest botnet problem, but it’s roughly in-line with the global average which sits at around 5-10% of domestic computers that are thought to be linked to botnets. Greece and Israel were way out on top, though, with around a fifth of all broadband subscribers thought to be unwittingly recruited into botnets.

It goes without saying that the biggest ISPs have the biggest botnet problem. And BBC figures indicate that the level of spam on BT’s network peaked at the end of July 2010, at which point more than 30m junk email messages were being sent each week.

Botnets2 520x269 More than one million UK households are part of cyber criminal botnetsThe good news, however, is that these figures have fallen sharply since then with a number of anti-cyber crime groups helping to bring down some of the biggest botnets. One takedown earlier this year saw spam fall massively overnight, when just an entire network, called Rustock, stopped sending junk.

As we wrote earlier this year, Microsoft effectively killed off the Rustock Botnet back in March, and then later offered a £250,000 reward for fresh information on how it came about. However, while the botnet itself was taken down, it left behind hundreds of thousands of infected machines around the globe.