A researcher named Igor Franchuk has discovered a weakness in Microsoft Windows, which can be exploited to hide certain information.
The weakness is caused due to an error in the Registry Editor Utility (regedit.exe) when handling long string names. This can be exploited to hide strings in a registry key by creating a string with a long name, which causes this string and any subsequently created strings in the key to be hidden.
Successful exploitation e.g. makes it possible for malware to hide strings in the "Run" registry key. However, these hidden strings created after the string with the overly long name will still be executed when the user logs in.
http://secunia.com/advisories/16560/