For impossible viruses that hijack your system, we recommend this very powerful tool: ComboFix

For anti-spyware needs, we recommend using MalwareBytes.

For an all-purpose all-in-one security solution that handles viruses, spyware, and malware, we recommend using Microsoft Security Essentials.

We have created a computer usage policy to be used throughout your company if you wish to implement it.  Just change the company name with your own and have each employee, intern, or contractor sign it. usagepolicy.doc