Anti-virus software might be useful, but I find that they tend to slow down the computer a lot. So I don't use anti-virus software, instead, I do these things to make sure that I can get back on track soon after my computer got malware.
1. Make sure you have recovery disk so you could do reset to factory default in case of virus.
2. Use windows system restore to restore the computer to a previous sane state.
3. I use AxCrypt to password protect my text file, even if the virus could transmit any file over the Internet connection, my critical personal info won't be hacked as it is password protected.