I have been using Mathematica 9 available as a shared application from the university where I teach. I installed a trial version of Mathematica 10, decided it was not worth the money, and uninstalled it when the trial ran out. I have since discovered that the uninstaller does not do a thorough job of cleaning the registry and has left behind some code that sporadically tells me my license has expired when I run Mathematica 9. I can clean the registry manually if I have to although it's a pain. Will this get rid of the offending code also?
By the way, hardly "malware" in any interpretation of the term... ;-)
David's suggestion should also work, since doing what he suggests puts a new entry in the mathpass file (and probably a bunch of other stuff).
The old activations seem to stick around, though. However, with the current activation in the first line, the older stuff is ignored.
Not sure how network licenses work -- or where things are on windows, but I think you have to do is edit the mathpass file. This could be opened with any text editor, and has the license info. In my case, I sometime had to edit this after testing beta versions.
The file is in the Licensing folder/subdirectory inside
$BaseDirectory or $UserBaseDirectory. (Both these are Mathematica commands, and return a path to the appropriate directory on your system.)
Once you open the math's file, you may see a reference to mathematica 10. If you delete this line, Mathematica will not use the temporary license anymore. (Make a back up copy just in case, of course.)
There may be a FAQ on the Wolfram site that explains this in more detail, or does more handholding.
As I said, I had a similar type of problem, and editing this file did the trick.
I don't know much about Windows systems... but perhaps the issue will go away if you reenter your activation key in your Mathematica 9 via the Help>Enter Activation Key... menu item.
Help>Enter Activation Key...