Your passwords to University computer systems are property of the University. The University has entrusted you with these confidential passwords, and only the University can authorize the disclosure of these passwords to anyone else. University policy is that your password is to be disclosed to nobody else, period. A user who discloses their password to another user can be subject to discipline, as can a user who logs in with another user's username and password.
Most dislosures of passwords are due to phishing. In phishing, a user is deceived into disclosing their own password to someone else. Phishing is a serious threat and is discussed at length in our phishing page. Other typical scenarios include supervisors asking subordinates for their passwords, or supervisors sharing their passwords with subordinates so that the subordinate can approve documents on the supervisor's behalf or read the supervisor's emails. Understand that these practices not only violate University information-security policy but also violate System policy regarding fraud and separation of duties.
When User A discloses their password to Person B, Person B can now log in as User A and view any confidential information to which User A had access. This results in several problems. First, Person B may be malicious and misuse the confidential data to perform identity theft, which harms the people (i.e., the 'owners') identified in the confidential information. Second, if the owners of the confidential data are harmed by the unauthorized disclosure, the University may be subject to fines and lawsuits. Third, even if confidential information is not misused, the University typically is legally obligated to notify the owners and various government agencies of any such unauthorized disclosure, which is time-consuming and damages the University's reputation.