OS2 is mentioned in an article about fight against activation problems with Windows:
"Use OS/2 instead. No activation issues. Microsoft has false positive results for legit versions of XP and Vista that appear to be pirate versions when they are not. Then Microsoft asks the user to buy a new software key because their original key appears to be greylisted as possible pirated. Not to mention they might have caught a virus that stole their key and posted it on the Internet and it got blacklisted."
Full article can be found at TalkBack.