Have you ever suspected your PC of doing stuff behind your back, talking to people it should not? Is it leading a double life?
Is your computer slavishly following orders from a remote master?
It is tempting to think your "personal computer" should obey only your instructions. It should do exactly what you want it to, not what anyone else does, surely...
But there are many more ways into your computer than just the keyboard and mouse.
Most importantly, there is your internet connection. This is divided into thousands of ports - in effect, doorways to your PC.
There is one for e-mail, one for your browser, and about 65,000 others handling more boring, day-to-day stuff.
And with the advent of broadband and "always on" network connections, they can get very busy indeed.
It is through these ports that attacks are made against your PC.
Protecting it should be those firewalls that Click Online is always harping on about. They are the equivalent of guards, deciding who to let in - and what stuff to let back out of your computer.
If you do not have a firewall that is correctly configured, or even turned on, you could be allowing malicious programmes to run on your computer.
This malicious kind of software - or malware - might not actually do much at all.
It probably will not go berserk and crash your computer, or wipe your hard drive. It may just sit there, listening, waiting for further instructions to come in on one of those unguarded ports - until the inevitable happens.
It receives remote orders, which it immediately obeys. In other words, it has become what we call in the trade a zombie.
Armies for hire
An average zombie PC looks like any regular computer: it doesn't eat flesh, groan or have aspirations to appear in a Michael Jackson video.
But while you go about your business, your machine is slavishly following orders from a remote master... sending out spam worldwide, or trying to bring down websites.
One zombie pc doing this on its own would be bad enough. But there are hundreds of thousands of them, all working together in armies called botnets.
These can send out billions of spam e-mails: in fact 70 per cent of all spam is generated by botnets.
As Google and Microsoft recently found out, the botnets can also bring down websites - by bombarding them with thousands of requests every second.
These botnets are now up for hire. People with the right kind of money and contacts can rent such services to do their dirty work. But who would want to rent them and why?
To find out, we spoke to Detective Inspector Chris Simpson from Scotland Yard's computer crimes unit, and Paul Wood from internet security experts MessageLabs.
You can watch the interview - which also explains steps you can take if you are affected - by clicking the video link in the box above.
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