If you do not have anti virus protection. We highly suggest you get one! They are inexpensive and it will help protect your system.
However if you suspect a file being infected and your virus protection did not detect anything.
Upload the file to virustoal.com. This website is very useful and it has save us many times.
Basically once you upload the file. It will scan 32 different antivirus database for cross reference. Some include Microsoft, McAfee and Symantec.
Try it, it is free and it is extremely helpful.
