Windows Defender - Virus and spyware definitions couldn't be updated

me too have this problem. pls resolve my issue soon.

https://www.microsoft.com/en-us/wdsi/definitions

If you go to the link, scroll down to the bottom and pick which applies to your Windows install (7, 8.1, 10) (64bit or 32bit) and just download it(click the blue text), look in your Downloads folder (or whichever folder you normally download to from your browser) and double click the file, it will update your Windows Defender to the latest version.

Then just follow steps i posted a couple above this to run the Windows Defender Offline Scan and your sorted, all your updates will work again.

I don't know how to do the instructions

Troubleshoot Windows Defender Update Issues in Windows 10

See the ANSWER of quietman7 in this thread:

https://answers.microsoft.com/en-us/protect/forum/protect_defender-protect_updating/windowsdefender-wont-turn-on/c502c63f-2ffe-4cfd-8b6b-bdfd086cfae0

https://support.microsoft.com/en-us  Note that this is the only “official” MS Support site. There maybe a charge for their assistance.

https://www.howtogeek.com/220232/how-to-use-the-built-in-windows-defender-antivirus-on-windows-10/  A good article but ignore the ads.

Or

If you cannot resolve the issue you are encountering with Windows Defender you may prefer to use a third party antivirus program….

There are a number of viable free and paid options available – take your pick…

Choosing an Anti-Virus Program

http://windows.microsoft.com/en-US/windows/antivirus-partners#AVtabs=win10

Good luck...

http://blog.emsisoft.com/2015/01/27/top-10-ways-pups-sneak-onto-your-computer-and-how-to-avoid-them/