Default Homepage and Search Engine Keep Changing

1. If you had a browser hijack, all the virus/malware etc will not find it.
2. Look at the properties of the Icon for IE. I had one situation recently where the home page change was added onto the exe. that took me a while to find.(about 1 percent chance of that being it).
3. It would be unlikely to be a hijack as they want you to use their home page and search engine. UNLESS you are not getting to the real MSN home page or Google search engine.
Just some random thoughts.