I have been using free version of Kaspersky on some Windows 7 machines and they recently got an update.
This was done automatically but when it came to updating the definitions they only got as far as 80% and stalled.

I spent a few hours on this, thinking I would have no Kaspersky.

Then I had a thought. Uninstal the new version without saving anything and then instal it fresh from Kasperskys site .
This was the answer and the programme installed fine and then the definitions.

I posted here in case some other users were having the same issue.