Number of followers

Aug 31 at 5:06 PM
Hi. I have done a Twitter User Network Search, and I found out that the resulting list and graph only show 2000 followers (out of more than 4000). I have repeated the search for an other +4000 Twitter User, and the number of followers that was given to me was also 2000.
Is there some sort of limitation on the search?
Thx