Just having an Anti-Virus program isn't enough.
Some tips:
1) Occasionally check that your "virus defintions" are up to date. All anti-virus progams do updates and date stamp them. Open up your A-V program and check.
2) Take care regarding attachments. Especially avoid opening attached files with extensions like .EXE, .SCR, .VBS and .PIF
3) Beware of "Phishing" scams that tell you there is some problem or other with your UTORmail account. The scam will ask you to type in your UTORid and password. The link offered in the scam is usually obviously not a UofT address. An example: utoronto-ca1.webs.com.