Its essential these days if you are running a PC with Windows to have some form of antivirus software running on your computer. Especial if your computer is conneceted to the Internet for browsing or email. While you can purchase software such as Norton and Kaspersky to do the job, there are some free antivirus packages out there which can be just as good. Two of these packages are AVG Antivirus and AntiVir. Although now Microsoft have joined the party with Microsoft Security Essentials this seems to work well and I have been installing it on any newly purchased computers recently. These all scan for viruses and spyware/adaware to keep your computer as free as possible from the nasties on the net. They will also inform you of phishing sites (sites that try to get your usernames and passwords by masquerading as being legitimate). Other free software for scanning for spyware/malware is available in the form of spybot, but this software need to be manually updates and used on a regular basis.
Excellent artice here at Moneymunk.com about phising and ID theft.