Muslims in Terroristic Organisations: How Many?

How many Muslims are involved in terroristic organization?

I realize that the best info will be only estimates.

I googled but the number of hits is astronomical.

I’m debating, (still).

Help!

I found this terrorismanswers.com where they quote Bush II as saying that there are thousands of Islamic terrorists.

A pretty wide amount of variance in thousands though.

I believe this is a completely unknowable question, at least in a GQ format.

First underground organizations rarely have proper membership lists, so it is impossible to objectively verify.

Second, there are rarley hard boundries or standards upon which to judge “membership” or even association.

Surely some reasonably reputable authority has an estimate. (?)