Hidden is the eleventh Special Ops level in Call of Duty: Modern Warfare 2 and it is in the first in the Charlie tier of operations. The objective is to reach the extraction point, silently eliminating any enemies you find or avoiding them altogether along the way.
Hidden takes place in Chernobyl (after the disaster), and the player must navigate their way to the extraction point, which is where the level "All Ghillied Up" began, from the shipping container area, passing through heavily infested radiated areas. The player begins the level with a suppressed Intervention and a silenced USP .45 with Tactical Knife. There are silenced weapons at the start that are able to be picked up as well: the MP5KSD, the Mini-Uzi, the M1014, and the Striker. The game keeps track of how long the player takes to reach the extraction point and is also ranked on how efficiently they kill each individual enemy; the system used includes "Perfect" kills, "Good" kills or "Average" kills. This will not affect the star-based score that the player receives at the end of the mission in any way. The number of stars is based on the difficulty the player completed the mission on, regardless of the type of kills that one accumulated.
Grenades are very useful in taking out the Ghillie snipers. If the player wasn't noticed before throwing the grenade, and a sniper is killed by a grenade, it will still count as a Perfect kill.
Type of enemy/ type of kill
The player must kill a soldier without being noticed
The player has killed a suspicious soldier
The player has killed an aware soldier
The player must kill a sniper without being noticed
On Hardened and Veteran difficulties there is a sharpshooter in the church's tower. However, his behavior is the same as that of a regular guard, not a ghillie sniper.
PC players can use console commands to NoClip outside of the playable area, and since the whole map was ported from COD4 to MW2, the player can follow the entire route that is taken on the mission All Ghillied Up, all the way to the end and further into the Chernobyl factories.
When outside of the map, following the All Ghillied Up mission route, if the player goes up the fire escape to the top floor, the player can enter a window and inside is a poster of Tanya Pavelovna, a character from Call of Duty: Finest Hour. 
If the player continues further along the All Ghillied Up mission route, they will eventually pass by where the wild dog would be feasting on a dead ultranationalist, and enter the Complex. What is notable about this area is that in COD4, all of the upstairs rooms have their doors closed and cannot be accessed, but in this Spec Ops mission, the doors are open revealing fully modeled rooms that have televisions that can be destroyed, along with water bottles on top of tables. Many players have questioned the reasoning behind the developers purposefully making this odd change to an intentionally closed off portion of the map, but there are still no answers to this day.
The player's character model will become blurry when they go prone.
All TVs in the map can be interacted with by using the use button, they will turn on and show a blank RGB Color test screen.
There are four TVs across the map; three in the main building in Chernobyl and one in a shipping container in the junkyard with the BMPs and Hind helicopters.