Most likely it is a Virus or a Malware. So far I have not come across any Windows 7 Operating System bug related to this problem. Please check the below mentioned link for steps on how to scan your computer for Viruses and Malwares:
Automatic account creation is mostly done by a virus plugin. Check your antivirus tool and update the software. Uninstall any suspicious program running in windows Control Panel. When this is done clean junk files/codes from windows registry/cache. Perform a system restore to the date when it worked fine and then perform advance system scan with the help of pre-installed virus protection application. If your security application is not strong enough then reinstall some other protection tool like Norton Antivirus, Immunet Antivirus, Kaspersky Antivirus, Bitdefender Antivirus, Avast Antivirus etc. Hope this helps.