A computer worm that spreads through low security networks, memory sticks, and PCs without the latest security updates is posing a growing threat to users.
The malicious program, known as Conficker, Downadup, or Kido was first discovered in October 2008.
Although Microsoft released a patch, it has gone on to infect 3.5 million machines.
Experts warn this figure could be far higher and say users should have up-to-date anti-virus software and install Microsoft's MS08-067 patch.
According to Microsoft, the worm works by searching for a Windows executable file called "services.exe" and then becomes part of that code.
It then copies itself into the Windows system folder as a random file of a type known as a "dll". It gives itself a 5-8 character name, such as piftoc.dll, and then modifies the Registry, which lists key Windows settings, to run the infected dll file as a service.
Once the worm is up and running, it creates an HTTP server, resets a machine's System Restore point (making it far harder to recover the infected system) and then downloads files from the hacker's web site.
