Monster Spawner

Monster Spawners (sometimes called Mob Spawners) are cage-like blocksspan style="font-size:13px;"> that were added in Update 0.9.0. They act as in their name; mobs will spawn around it in a certain radius. It contains a spinning image of the mob that spawns out of it, which spins faster until its mob is released and repeats the process.

LOCATING
Mob Spawners are mostly found in Dungeons, Strongholds, and Abandoned Mineshafts, accompanied by Chests containing various items and are presumed to challenge the players that try to raid the chests.

Disabling
To disable one you must put 4 torches on the side or just 1 torch on the top of it. For some monster spawners, (such as Passive Mob Spawners) you cannot disable them without breaking them.

Trivia

 * Since Update 0.9.0, it will spawn hostile mobs in survival mode, in dungeons, strongholds, and mineshafts. Dungeons will have Zombie, Skeleton, or Spider spawners. Strongholds will have silverfish spawners. Mineshafts will contain cave spider spawners.
 * In Creative Mode, you can change the spawner to spawn any mob you want by using a spawn egg (a Minecraft PE exclusive feature.)
 * Dungeon spawners have a higher chance of spawning Zombies (50%) compared to Skeletons and Spiders (25% each.).