I'm having the same problem and apparently it's widespread. I have an Asus which was originally Windows 7 and it automatically updated to Windows 10 while I was not using it. I have never used Norton nor McAfee. The Version is 1606 and the OS Build
is 14393.1593. I thought I fixed the problem by doing a ChkDisk but apparently not.
Cannot update windows defender virus definition file ,
Answer by the numbers .
1. 2013 , I think .
2. No , updated from Win 8.1
4. I don't remember .
5. I don't know . picked up a Virus about two years ago . Had on-line supposed computer tech fix my system that is when my problems began with system besides the definition file's other things wont down load ether , ex . Fox
6. Ver .1607 (OS build 14393 , 1593 )
I just folowed this thred to this help aria from Windows defender . If you can help me that would be great .