try using this program to uninstall it then install your proper version of MSE (be sure you get the one for your version of windows) free AppRemover utility since it is an xp computer you will need to be sure you do not get the 64 bit option. Security Essentials 4.2.223 XP Please check to make sure he is able to get windows updates and also he is able to create restore points. There is an infection we have seen that causes you not to be able to and it also disables the antivirus so just want to make sure. I would also install and run the free malwarebytes and run a full scan just to be sure. It is a program I think everyone should have on their pc, update an run the scan every couple of weeks. Malwarebytes' Anti-Malware (Win) - Detecting and Removing Malware directions Malwarebytes Anti-Malware 1.70.0.1100 Download download it from this link.

@harry_wild "know that in order to prevent a new virus or malware for your on going service; you have to get it from Microsoft in the first place!" You keep stating this, but provide no evidence. Why don't you provide some proof of it, if you think it's true. Just stating something doesn't make it true. . @ wolfie46 "Is there any problem running AVG and malwarebytes at the same time on a computer with windows 8.1?" Shouldn't be any problem. Although it would probably be a good idea not to run scans by each, at the same time.

I agree, it's definitely not necessary to uninstall the old antivirus software before downloading a new one. But before installing the new one, for sure. fredda, at the risk of stating the obvious, Windows XP is no longer supported from a security standpoint and using it does entail some risk. So long as you are using this PC for general purposes only and not for essential uses with any Win-only software, I would seriously consider installing Linux (a different operating system that's available for no cost) to replace XP. Start a new thread on that topic if that may apply to you, there are other contributors here (not me) who can provide helpful guidance.

The Avast free version is highly rated, the paid one not so much. Before buying anything, check with your internet provider. Many provide the better name products for free. Luck has little to do with whether your machine accumulates problems or not. It is much more dependent on users being thoughtful in their internet practices to avoid problems and also having competent security software installed. Objective ratings of AV products Objective ratings of free AV products