I often work on folks computers which have a variety of anti-virus programs that may be expensive as well as basically ineffective. Windows is vulnerable to a wide scope of intrusions which include viruses as well as malware.
Why spend on programs when Microsoft offers a free anti-virus at Free Virus Protection with Microsoft Security Essentials This program runs automatically and is constantly being updated. It will trap most viruses before they have a chance to do any harm.
Another problem in Windows is the Potentially Unwanted Program, called P.U.P. and is insidious. These things come in on downloaded programs so be careful when you download anything to read all the text on the pages to exclude any of their options. Tool bars, recipes, coupon sites, adult sites, games, music, etc. are prime providers for these PUPs which actually grow in your computer until it no longer functions.
To scan for PUPs get Malwarebytes Anti-Malware - CNET Download.com You might be amazed at the number of objects it will find. This is free to run but may ask for a payment after 30 days.
To get rid of all those toolbars that seem to come out of nowhere, go to your control panel and find add/remove programs. Most toolbars will be listed there.
To do a thorough clean-up of your computer files you will need to clean the registry. Every page you visit plants a notation in the registry as well as a temporary page in your memory. To do an efficient clean up get Glary Utilities - Free System Utilities to Clean Registry, Fix ...
This is the best I have seen for the job but must be run manually. It is simple and fast so try it today.