Hash rules are rules created in group policy that analyze software. It considers the “footprint” of software to recognize it. This means that if the program is renamed, it will still be recognized. Renaming the software is an old trick used by people who write viruses. these hash rules in Group Policy can be used to either allow or disallow a program to run. The problem is that if the software is updated or the users simply download an old version, the software can run. This hash rule and many like it can stop a virus or trojan from running rampant in your network. This is available in local or domain group policy, although this video is made using the local GPO. It affects all users of that computer. This video was made on Windows 7, but is possible on XP, Vista, 2000, Windows Server 2003 and 2008.