I just installed and ran Malwarebytes free per Riley’s tip, and it found six items that it removed with my permission. I recently installed CCleaner, and I use Kaspersky Internet Security. I have never had any viruses with Kaspersky, but I have with Norton.
I’m not big of the two giants, Norton and McAfee, but I guess they’re adequate if your definitions are kept current. I have more experience with McAfee, I think I recall that they update every day. Kasperky has a pretty good reputation, but anti-virus software is always reactive, not proactive, so there will always be a window of vulnerability.
Self-installing utilities like the one you’ve described are not always true viruses or detected as such. Techs often refer to this sort of thing as ‘crapware’.
The thing that’s kept me clean for years is that I run my web browser with a script blocker. (Firefox with the NoScript plugin). Certain sites that you *know* are clean, I ‘trained’ NoScript to not worry about. Anything else I go in with everything blocked and hit the option to ‘temporarily allow all this site’ if I think it’s clean. The other major vector for this stuff is email. I use one of the major services, and I am highly suspicious of mail from friends that...doesn’t seem right, and I don’t open it. The service has been fairly good at screening attachments and links for malware and spam. I pull it down to a POP client so I have a record of my mail.
CCleaner is a staple, and has a wonderful, easy interface for managing startup programs. Love it. I bought the paid edition of MalwareBytes, and you can automate everything- updating and scans and so forth. Worth it to me.
Things have come a long way from the days of having to ‘freeze’ the kernel and identify and manually unhook malicious DLL calls. :-)