When CQ University's computers began acting sluggishly, computer operators were relieved when a software trouble-shooter from DELL called. When he offered to correct the problem they were having, he was given a login ID and password. The next morning, the computers were worse. A call to DELL confirmed the university's suspicion: someone had impersonated a DELL repairman to gain unauthorized access to the system and destroy the database. CQ University was also concerned that the intruder had devised a program that would let him get back into the system even after all the passwords were changed.

What techniques could the imposter have implemented to breach the university's internal security?

how can i answer?