A noobtubber is a person who uses grenades to kill others on CoD online?

If they're able to kill you then why are they called "noobtubbers" ?

I don't own MW2/BO atm because there are games with far more priority than just shooting games.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).