I cant download yahoo messenger it keeps show warning that may harm your computer

I hate to assume anything, but the problem is NOT that computer, in as much as it is simply following the user prompts of what to do in a situation, such as giving some website access to your harddrive.

In reading your question, it merely sounds as though your anti virus, or windows security software is warning you that an attempt is being made to download software.

You'll need to provide more information to better ascertain if there is more of a problem. However it sounds as though this is the case,

Perhaps during the process, you're hearing a belltone (warning beep) and maybe you have not looked to see it, but there may be a light yellow bar displayed horizontal across the top of your window, under the browser toolbar above. If you right click on this, it may be suggesting or asking for you to decide to allow this operation or not.

In either case, you should be able to allow the operation simply by approving this action as OK.

Good Luck

Respectfully

I guess you are trying to download it from Google Chrome, if so, it's not actually going to harm your computer, but as a precautionary measure, it only warns you, suppose if in case something is trying to download without your knowledge, this will prevent it from downloading automatically. Simply click "Yes" and download it. If you are not very sure, please follow this LINK and follow the instructions on how to download and install Yahoo! Messenger. Let me know if you need further help.
Good Luck.
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