After some searching I found this, but cannot verify if it is true or scuttlebut

QUOTE
An unregistered version of windows 7 or a Release candidate(RC) version will shutdown automatically at random interval of time.
UNQUOTE

Also there was a whole bundle of Win 7 SW that was illegal, but legitimate traders were caught selling pirated copies. (As well as the shonks deliberately ripping off people.)

If you did not attempt to register (illegal copies with false IDs will fail the registration) then you may not be sure whether it is a valid copy.

Also if you did not register, then security updates probably not happen after a while, thus you could have got virused anyway.