Aephus was a turian colony that had a major shipyard. Cerberus targeted it for attack during the Reaper invasion in order to capture the shipyards, but volus ambassador and former Cerberus informant Din Korlack learned of the attack. He was captured by bounty hunters including Zaeed Massani (if Zaeed survived the suicide mission) after the turian government put a bounty on him after learning of his involvement with Cerberus. After he was rescued by Commander Shepard, Korlack was reluctant to give up the information on the attack in case Cerberus learned he had betrayed them.
If Shepard managed to convince Korlack to give up the information, the turians received enough warning to prepare for the attack and repel Cerberus.