Hamachi is a very useful application that helps establish a link to other computers over the internet that emulates a LAN. Basically put, it makes your computer think that a network over the internet is a Local Area Network (LAN). Why is this useful? Well the reason I use it is to help create multiplayer games in Rainbow Six Vegas 2. Vegas 2 doesn't use dedicated servers (Modern Warfare 2 anyone?) and knowing how buggy and glitchy Vegas 2 is on network connections being made, using Hamachi to make Vegas 2 think you're playing with others on a LAN makes it convenient. Not only does it connect you to the host 100% of the times, you don't have to sign into your Ubisoft account (you still have to create an account to start the game.) You can use Hamachi for other games too and the brilliant part is that you play with people that you trust (obviously since you have to give them your server information that you created with Hamachi.) Since this program does connect you to another person's computer, there are certain security risks involved so you have to be careful with who you give your info to.
So, for those that would like to use Hamachi, you can go here to download it: http://filehippo.com/download_hamachi/
and for instructions, I have listed a link to help you install it and get it ready.