I have been seeing a lot of easily answer questions being asked time and time again in the keygen threads, so I thought that I may as well make a small guide on how to keygen and check the resulting keys, from start to finish.
Sections:
1) Programs and other requirements
2) Generating the keys
3) Checking the keys
4) Using a 'good' key
1) Programs and requirements
You'll need a few programs to do this. Firstly, you'll need a keygen. Secondly, you'll need a keychecker, and thirdly you'll need ArmA 2 Operation Arrowhead (It does not matter if it is a steam version or not, everything is the same for every version of ArmA 2 Operation Arrowhead). I recommend putting all the required programs in a separate folder, called 'ArmA Keygen' or something similar. I also use a text-splitter, you'll see why.
First off, the keygen. The most important thing for keygens is speed, and JavaEEcrack's keygen is the fastest by far.
Secondly, the keychecker. Currently, the only one we have is Darky's Keychanger. It's slow, but it's the only option.
Lastly, the text splitter. I use Simple Text Splitter. Any text splitter will do, I guess.
2) Generating the keys
First off, fire up JavaEEcrack's Key Generator. It will pop up with a messagebox asking for the amount of keys you want to generate. I reccommend 1 million, but anything below 500,000 almost certainly probably won't get you anything at all.
Once you have decided, hit enter and wait for it to generate. When it has finished, it will say "Done!", and there will be a text file with a random name in the same folder as the keygen itself. This file contain all of the potential keys.
3) Checking the keys
This is where the text splitter comes into play. Open the text splitter, import the text file generated in step 2, and split into 4 parts.
You will now have 5 text files. Feel free to delete the original, because we're using the split files.
Next open Darky's Key Changer four times, and navigate to the Ban Checker/Key Checker tab on each one. Make the check type Key Check, and click the import button. Import one of the split text files into each of the 4 key changers. Then, change the 'delay' to 10, and wait until you can click the 'Check' button. When you can, hit it and wait.
And wait.
And wait.
I reccommend leaving this overnight, it may even take 24 hours, and you must have an internet connection for all of this time. When Darky's Key Changer has checked all of the keys, it will show the results in the black box. If it says that you have a valid key, then congratulations! You've nearly got yourself a free ArmA 2 OA CD key. However, we must do one more check.
You must now search through the list of CD keys in Darky's Changer, looking for the valid CD key. It will have a green 'valid' symbol next to it, as opposed to a red 'not valid' symbol. When you find it, note it down on a piece of paper, and change the 'Check type' to 'Ban check'. Then type the key into the 'Single Check' box, and hit enter. If it's not banned, then congratulations! You have a vaild, unbanned ArmA 2 OA CD key! Now, how to use it...
4) Using the key
To replace your current key with your valid, not banned, generated key, just type the generated key into the box in the 'Key Changer' tab of Darky's Key Changer, and hit enter. Your CD key has now been changed to the generated key!
Hopefully this has helped at least one person. If you have anything to add, or you have spotted a mistake, please do reply. Have fun with your keygens!