I had the same experience a few days back when a software that I was trying to install also installed IncrediBar, which is a Browser Hijacker Object. To my horror it promptly hijacked all my browsers and try as I might I just couldn't get rid of it, like you can't "alot".
The day was saved for me by restoring the latest earlier image. I recommend that you do the same. We make images, only to get bailed out of these tricky situations.