How to Check if You Have a Virus on Your System

If funny things happen when you are installing applications or if they do not run as expected, first thing to check is if you have a virus on your system.

The most common manifestation of a virus on your system is when files start getting corrupted.

Viruses commonly corrupt executable files and DLL files on your system when they are created or accessed. So any suitable file that you download from the Internet could probably be infected. Here are some steps to check before firing up that virus checker and checking your whole 80GB hard disk.

1. Get a nice MD5 checksum utility like WinMD5
   
2. Download an EXE file - WinZip installer comes immediately to mind - and save it to disk.
   
3. Download the same file again, BUT save it as a .TXT file. Yes, as a TXT file, because viruses normally DON'T infect non executable files, and they usually only tell by the file extensions.
   
4. Drag and drop the two files into the WinMD5 application window, assuming you have opened it in the first place. If the checksums don't match, then you are in trouble. Perform a full virus scan - there are some online scanners available - on all files and folders on all drives. Delete all affected files.
   
5. Despite 'common wisdom' advising to the contrary, you can still install and run an anti-virus program even if you have been infected with a virus. After all, this is the best you can do at this stage. I've tried McAfee evaluation version with good results.
   

If you are unwilling to shell out the bucks for anti-virus software, try AntiVir Personal Edition.