Your antivirus program, providing you use a decent one and keep it up to
date, should warn you if a virus is downloaded. Check your program's
documentation to see what the warning looks like.
Here is a link to the EICAR Test string. This is not a virus but a way to
test your AV to see how it works http://www.eicar.org/anti_virus_test_file.htm Make sure you read the
information and disclaimer first. If your AV program places viruses it can't
fix into a "Quarantine" then you will need to open that Quarantine and
manually delete EICAR from it. If you download EICAR make sure you delete it
out of the recycle bin or it will trigger your AV program everytime you do a
full system scan.