An antivirus program
and as much antispyware as you wish
You can either buy a suite containing all three or get separate programs for each.
Easiest is buy a suite such as Norton etc.
You will pay for the privilege and keep on paying an annual subscription but you get support.
Harder is to buy separate packages that will actually work with each other.Buying means you get support.
Or you can download separate packages FREE but not get any support. Other than what we can give in the Helproom.
Many people on the forum have their personal favourites.
My FREE recommendations are:
Firewall - ZOnealarm
Antivirus - AVAST
Antispyware - SpywareBlaster as a blocker
Windows defender as a realtime scanner
AdAware as a backup scanner
All work well with each other and do not take up many resources.
I will provide links if you want them.