Green AV or Green Antivirus is one of a number of software programs that are really rogue antivirus or antispyware.  They claim to be there to protect and keep your computer safe from viruses and spyware, but in reality they manage to install themselves via very shady methods.  (I suspect that you may not know how this program came to be on your system for instance.)  These programs will also claim to find problems with your system and only offer to solve them for a subscription fee.  Many legitimate antivirus vendors do charge subscription fees to maintain their virus database, but you should realize that this is a slightly different practice than charging to remove a virus that it knows (or claims) is on the system.

Green AV is simply the latest in a long line of such rogue security software programs (see my Remove Windows Police Pro article)  and as many it can be a pain in the neck if you have it installed on your system.  It is likely that it will be constantly popping up messages warning you that you need to subscribe to protect your system.  It may be exhibiting other behaviors as well, but all of them likely are aimed at scaring you into paying their fee.

It can also be hard to trust when you see so many free removal tools floating around for these rogue security programs because it's completely likely that the program originally billed itself as a free download.  (Very few bill themselves as a painful expensive ordeal do they?)  So, the best ways to remove these pests such as Green AV is manually and with the use of other trusted antimalware programs.

Instructions to remove are similar to those for other rogue security programs. First you will have to disable the running instances of the software via the task manager. It may also be necessary to boot into safe mode. I would probably try the following steps first by starting to kill off processes related to gav.exe gra.exe or greenav2009.exe or anything similar and then see if I could delete or rename the files without rebooting to safe mode.

If you choose or need to boot into safe mode, then delete or rename C:\Program Files\Documents and Settings\All Users\Application Data\GAV\gav.exe since that's the main program executable.
Look for mgrdll.exe and delete it and also take out the \Application Data\GAV folder.

From what I see, for some users they may find GRA instead of GAV for the filename.

Green antivirus 2009 may also go under the name greenav2009.exe in the process manager. Look for anything similar or related to this name if you can't find one of the items specifically mentioned.

Also if it is named differently than above look to delete or rename the files that you find acting as green av to successfully remove it.

After you have a "foothold" of sorts and have made some progress against a pest like this continue to make sure you get respected malware removal like malware bytes antimalware, sypbot, AVG, etc. on the system and update them, run full scans and test with a few reboots to make sure the baddie doesn't resurface.

You may also visit my Green AV Remove lens.