Though the threat posed by computer viruses -- small software programs that can harm your programs and data -- is sometimes overblown in the popular press, it is still real. As the Internet has developed, so has the frequency of virus attacks and the ways they can infect a computer. Viruses can attack via email, via security breaches in the operating system, and other ways.
Virus protection software works at many levels. It can scan every disk you put into your floppy drive and check every program for a hidden virus -- before you run the program. It can even scan all the files on your hard disk for viruses. With the viruses being sent via email nowadays, users should configure their virus utility to run when they start up their computer.
If you do not have an anti-virus utility on your computer, you should go to one of the online antivirus utilities to scan your system.
Trend Micro Housecall - will scan and remove threats
BitDefender Scan Online - will scan and remove threats
Ewido Online Scanner - will scan and remove threats
Panda Activescan - appears to only scan for but not remove threats
McAfee FreeScan - appears to only scan for but not remove threats
eTrust Antivirus Web Scanner - will scan and remove threats
Symantec Security Check - will scan and remove threats
Dr.Web Online Check - user can upload and test for threats on particular files
You'll also want a good anti-spyware program to help rid your system of spyware, malware, and adware. The best one in my opinion is MalwareBytes AntiMalware, you can download and use the free version or purchase the full version that allows real-time monitoring of your system for spyware.
If you don't already have antivirus software loaded on your computer. You should download and install an antivirus product immediately. The popular commercial antivirus products like McAfee and Norton are ok, but there are also excellent free antivirus solutions available. Listed below are some of the popular free and commercial antivirus software products.