There's no such thing as "good, free" antivirus.

£30 a YEAR will get you Kaspersky Antivirus, and with that you get a 30 day free trial to make sure it works on your machine and tie you over to pay day, and protect you while you umm and aah over whether or not you want your machine to actually be secure.

Go to www.kaspersky.com and get your wallet out.