A free antivirus product does not adequately protect you from the dangers of the internet. The free product has not got the real time functionality where it prevents viruses entering your computers !!
It is best to protect your computers with a fully functional registered virus checker.
Beware of telephone callers claiming:-
to be from Microsoft or that you require updates to be loaded.
that you have a virus in your computer and that you require to purchase an antivirus program.
that they are from your bank and require you to logon into your bank account .
These callers are actually Cyber-criminals attempting to get credit card details,personal information and banking usernames and passwords from you. DO NOT ENGAGE in conversation. Hang Up the phone immediately.