If your web browser does not default to the home page that you set, you probably have malware. The one that affects Autodesk the most is Trovi.
If you are running an Autodesk product on Desktop Subscription [confirmed via C.Rothe], you will get the following error:
The revised solution for this issue has been updated here:
If you run AutoCAD 2015, you will get this error:
To effectively remove the malware, I would review the following blog post: