Why does my PC's processor run at 100 per cent even when idle?

Q All of a sudden my PC’s processor seems on occasion to run at 100 per cent, which stops me doing anything.

The computer is not running any programs and I can even switch off the modem, but still the problem persists – it can go on for several minutes.

If I turn off the computer and switch it on again, everything is normal again – but usually not for long.
John Morton

A The behaviour you describe is typical of the effects of a malicious software infection. Some viruses force infected PCs to join a wider ‘botnet’ that may be used for all manner for nefarious purposes, from mass spamming to
denial-of-service (DoS) attacks on the server computers of large corporations.

The suddenness of the problem’s onset further supports this idea, as your PC was operating normally previously. Moreover, when the PC is restarted there will generally be a few minutes while everything works normally, before the virus kicks in once more to connect your PC to the botnet. Turning off the modem may not help, because the virus will continue trying to do its dirty work.

Download, install and run a free scanning tool such as Spybot Search & Destroy to see if anything is found. Our hunch is that a Trojan has snuck its way onto your PC and is the cause of the problems.

Use Spybot to hunt down and remove any viruses and then apply the program’s Immunize function to your web browser to prevent future infection.