Gamal Abdel Nasser:

The crowd roared in approval and Arab audiences were electrified. The assassination attempt backfired, quickly playing into Nasser's hands. Upon returning to Cairo, he ordered one of the largest political crackdowns in the modern history of Egypt, with the arrests of thousands of dissenters, mostly members of the Brotherhood, but also communists, and the dismissal of 140 officers loyal to Naguib. Eight Brotherhood leaders were sentenced to death, although the sentence of its chief ideologue, Sayyid Qutb, was commuted to a 15-year imprisonment. Naguib was removed from the presidency and put under house arrest, but was never tried or sentenced, and no one in the army rose to defend him. With his rivals neutralized, Nasser became the undisputed leader of Egypt.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". To what group did many of the arrested dissenters belong?
Brotherhood