What is the ruling on hacking the accounts of some university colleagues with the aim of accessing information about a specific girl, and is repentance and cessation of this sufficient, or is it obligatory to appease the account holders, especially if this is difficult and the hacked individuals cannot be identified?

This intrusion is a forbidden form of espionage, and the girl's desire for advancement does not justify it. Rather, it is prohibited by His (Allah's) saying: "And do not spy." You must repent and seek forgiveness for what you have done. You are not required to inform the person you spied on about this, due to the potential harm that might result. Seek forgiveness for the one whose privacy you violated and supplicate for them. This is sufficient for your repentance, along with remorse and the firm resolve not to repeat the act.