I guess asking in the Malwarebytes forum might do you some good because they are supposed to be the experts.
Maybe this question should be forwarded or moved to the virus / security forum.

Either it is a false positive or your computer already was infected and is infecting the updates.

Have you received the same results from another anti-virus program?
Which virus does Malwarebytes detect? (I am not asking you to post a log.)

I am operating under the assumption that Microsoft doesn't make mistakes and transmit viruses.