Malware for PCs is an established part of life. Keeping the operating system and applications up to date helps (a vulnerability that's been removed can't be exploited), as does decent security software.
And if the worst comes to the worst, there's always the possibility of completely wiping the hard drive and starting from scratch.
But a security researcher has shown that a small malware loader can be concealed in the BIOS or other firmware built into a PC.
Jonathan Brossard demonstrated this approach at the recent Black Hat conference in the US. The routine hidden in the BIOS connects to a remote server to fetch the code that does the dirty work.
Unlike conventional malware, this leaves no trace on the hard drive for later analysis as the rogue code is freshly downloaded each time.