Valve has released a new Arms Deal update for Counter-Strike: Global Offensive which re-adds silencers to the game, adds several new weapon skins, and new weapon skin crates.
First up the update re-adds the silencer for the M4 and USP, both of which were removed for balancing reasons in Global Offensive–the difference now is that they must be bought separately and are not available automatically with the guns.
Next up is the new weapon skins, these can be earned via drops that you receive while playing the game, and can also be sold and bought by players on the Steam Marketplace. The skins can also be gotten through new eSports Cases, which require a key to open. A percentage of money from each case sold will “be redirected to fund prize purses at upcoming CS:GO eSport events worldwide.”
You can check out more details here.