So you can install the game on your PC at work with the same key. All you have to do is choose "online activation".
Authentication by going online
You can also choose to authenticate by going online once.
If so, this happens the first time that you start the actual game. You will be asked for permission. If you allow it, SecuROM will talk to a master server, which counts on how many computers your serial key is currently in use.
When the installation has been authenticated online once, SecuROM will no longer go online. You can then play the single-player campaign 100% offline, without needing the DVD. Also, you can play multiplayer online without needing the DVD.
You can have the game authenticated on up to 10 machines at the same time.
One authentication is valid for 10,000 days. Thus, if you authenticated once on launch day - March 2nd, 2010 – that authentication will be valid until July 18th, 2037.
More info in this topic:
http://blogs.battlefield.ea.com/battlef ... ction.aspx
