CCleaner is good, but in addition you should also have SpywareBlaster (http://www.filehippo.com/download_spywareblaster/) and Spybot Search&Destroy (http://www.filehippo.com/download_spybot_search_destroy/). Run both about once every two weeks. Be sure to update them first, use SB to keep your computer protected and SSD to immunize your computer and scan for possible threats.
And here's some Firefox add-ons I recommend to make your web browsing safer: AddBlock Plus (https://addons.mozilla.org/en-US/firefox/addon/1865) is something no one should browse the web without! Gets rid of those annoying advertisements on most web pages and protects you from the risks they pose. Web of Trust (https://addons.mozilla.org/en-US/firefox/addon/3456) tells you the reputation of the websites you're about to enter so you can avoid risky sites. And if you want to be very well protected, you'll get NoScript (https://addons.mozilla.org/en-US/firefox/addon/722) too, with it you decide which websites are allowed to run scripts so you'll get no unwanted surprises.
I'm using all of these myself too and haven't had any virus or ad/spyware problems in months.
Also, for a firewall, I hear Filseclab (http://download.cnet.com/Filseclab-Personal-Firewall-Professional-Edition/3000-10435_4-10421598.html?part=dl-Filseclab&subj=dl&tag=button) is a good free one.
After this you can safely surf for busty asian babes all you want ;P
And here's some Firefox add-ons I recommend to make your web browsing safer: AddBlock Plus (https://addons.mozilla.org/en-US/firefox/addon/1865) is something no one should browse the web without! Gets rid of those annoying advertisements on most web pages and protects you from the risks they pose. Web of Trust (https://addons.mozilla.org/en-US/firefox/addon/3456) tells you the reputation of the websites you're about to enter so you can avoid risky sites. And if you want to be very well protected, you'll get NoScript (https://addons.mozilla.org/en-US/firefox/addon/722) too, with it you decide which websites are allowed to run scripts so you'll get no unwanted surprises.
I'm using all of these myself too and haven't had any virus or ad/spyware problems in months.
Also, for a firewall, I hear Filseclab (http://download.cnet.com/Filseclab-Personal-Firewall-Professional-Edition/3000-10435_4-10421598.html?part=dl-Filseclab&subj=dl&tag=button) is a good free one.