User:Capry

Infested block as an item could be obtained in Beta 1.8 Pre-releases with endermen as well as Beta 1.9 Pre-release 4 with the introduction of silk touch. This item is able to be updated into the current version and still exists without converting or being deleted. The possible infested blocks that can be obtained are stone, cobblestone, stone brick, mossy stone brick, cracked stone brick, and chiseled stone brick.

Endermen
If backdating is not to be used (in which case you would backdate a 1.9 Pre-release 4-1 world where silk touch was used to obtain infested stone), a player must first locate a stronghold in the Beta 1.8 Pre-release versions to find infested stone. Then, to obtain the correct block, either getting the silverfish to enter the desired block or using block transmutation to obtain the data value desired (table below) on the stone. Next, an Enderman must be used to pick up the block, making the Enderman hold the infested block. To obtain the item, the world must be updated to 1.7.10, and then in 1.9 the Enderman can be killed, obtaining the item.

Silk Touch
Using any pickaxe with silk touch (including a fortune and silk touch pickaxe) on any monster egg during Beta 1.9 Pre-release 4 would drop an infested stone block. This only works to obtain the stone variant. The infested stone must either generate in a stronghold in versions beta 1.8 Pre-release and later or form when a silverfish from the stronghold's silverfish spawner goes into stone, cobblestone, or stone bricks. Note that the silverfish spawner only generates in a stronghold from Beta 1.9 Pre-release 3 and up. Cobblestone and stone brick monster eggs existed but would also drop the stone variant when mined. If all three locations of stronghold have been generated in previous versions then this will not be obtainable. Additionally, if all three silverfish spawners and all the infested stone that naturally generated in the stronghold are destroyed (and any remaining silverfish killed) then this will also become unobtainable.

Stronghold Generation
The location of all three strongholds cannot have been loaded in an earlier version. To test where the strongholds will generate you can get your world's seed, open up Beta 1.9 Prerelease 3 and make a world with the same seed in creative mode. Fly around and find the glass pillars that generate above strongholds in this version. Press F3, note the location of the stronghold, and then make sure you never enter that location until this version. If you have accidentally generated the area, you can cheat in MCEdit to delete the chunks where it should spawn if you wish.