Four categories of food and drinks prohibited in Islam :

1. Prohibited By Itself
This category comprises any food and drink prohibited by a clear text from the Quran.
2. Prohibited Due To External Factors
Any food or drink which is basically halal but transformed into haram due to one of the haram determining factors makes it prohibited. e.g. A halal lamb is becomes haram if its stolen.
3. Prohibited Due To Harmfulness
Any food or drink that harms human body or health.
4. Prohibited Due To Impurity And Filthiness
Any food or drink that is not clean and pure is haram. The goodness and wholesomeness of food and drinks are deteriorated by filth and impurity thus making them haram.

source: http://www.malaysiahalalfoods.com/haram.html