A Palestinian Arab agency says that the number of Arab prisoners in Israeli custody has decreased this year to 7350.
6124 are from the West Bank, 768 from Gaza and 458 from within Israel.
3600 of the prisoners are affilitated with Fatah, 1840 with Hamas, 1150 from Islamic Jihad, 450 from the PFLP, and 110 from the DFLP.
In July, the group Adalah reported that there were some 13000 Arabs in Israeli prisons. However, looking at their data a little closer it appears that if we only count the prisoners who are classified as security prisoners (as opposed to criminals) the numbers are pretty close. (In fact, Adalah mentions that there are 6500 Jewish prisoners as well.)
In June, 2008, the Israeli Prison Service said that there were 10,000 security prisoners.