Kingdom Hearts coded
Bug Blox appear in all of the Data Worlds from Jiminy's Journal; they are a product of the data "bugs" from digitizing the journal. The Data-Sora must destroy Bug Blox in order to progress through worlds and the storyline, as well as fix the Data Worlds.
In Episode 8, it was revealed that Naminé's manipulation of Sora's memories in Kingdom Hearts Chain of Memories was the primary cause of the appearance of the Bug Blox. The Data-Naminé confirmed this to King Mickey and the Data-Sora, along with informing them of the suffering of some connected to Sora's heart, namely Terra, Aqua, Ventus, Roxas, the real Naminé, Axel, and Xion.
List of Bug Blox
Each Bug Blox design has different characteristics which determine how it must be approached. Kingdom Hearts Re:coded added more types of blocks.