Matters such as tenure, salary, job performance or personal information such as social security numbers, or credit card numbers are not good candidates for email. If it is simply impossible to observe this rule, at least take measures to remove sensitive email from your account immediately, but don't get lulled into a false sense of security. Many systems run automatic file backups that copy your email without your knowledge. If you are especially concerned about this, you may wish to consult with your system administrator to become familiar with the backup methods in your particular environment. Don't jump to conclusions and take any drastic steps without first confirming the communication by phone or in person.
Strong passwords resist automated password guessing attacks.
Oftentimes, the easiest way to break into a computer is not through technical means, but through a scam or a confidence game. Be suspicious of unsolicited offers of technical help or advice. Also be alert for individuals posing as your system administrator asking for confidential information, or instructing you to take specific actions. These all violate Penn policies. In most cases it is possible to trace such abuse.