During an online game get killed and when your lying on the ground dead pull out your ethernet cord, when the gun selection shows up plug it back in. When you respawn no one can see you, and you will be invincible. If some one joins after you execute the glitch they can see you, but you will be invincible so don't worry they can't kill you. Don't abuse it because people get pissed off quickly and will report you so I would suggest using it once or twice a game. This glitch only works if you're the host.
These become unlocked depending on what stage your 'Game Save' file for Metal Gear Solid 4 is. If you have a 'Game Save' file of a completed game ALL the music tracks will become unlocked. Boss tracks will become unlocked when you have a 'Game Save' file after you have defeated them. If you have a completed 'Game Save' file and continue it in Metal Gear Online ALL the music tracks will be lost until you unlock them again.