The most important advice we can give anyone who believes he or she has a computer with malware on it is this: Don't panic. Also, don't assume that you need to wipe your computer clean and start from scratch. Often you can remove malware without having to erase everything else. You may lose some data in the process, but you probably won't lose everything.
First you need to determine if your computer has a virus at all. You might suspect your computer of having a virus if it seems to be sluggish. If your Web browser suddenly looks different or automatically goes to a site you don't recognize, that's a good indication that you've got some malware. If your computer is unstable and crashes fairly often, you may have a problem. And if you try to access files but receive a message saying they're corrupted, that's another sign.
If you do think your computer has a virus, you need to run antivirus software to weed it out. Some viruses disable antivirus software, they're clever that way. If you do not have any antivirus software, its a good time to purchase or download an application. A few malware variants will try to block you from downloading antivirus software. If that's the case, you may need to download the software on another computer and transfer it to disk or a flash drive.
After install antivirus software should update regularly and perform automatic scan or protection.