Q: Reminders brings up message: Reminders can't connect to the account "Exchange". This is not my account; it then requests a password for an e-mail address which is not mine. Can anyone help?

Go to System Preferences - Internet Accounts and look for the Exchange account there. Delete it if you don't want to use it.

Matt

Does anyone else ever have physical access to your computer? Does the address belong to one of your friends/family/contacts? Have you recently had to take in your computer for repair, or given remote access to anyone?

It's very unlikely that you have been hacked - a hacker does not normally add their own email address to your system.

Matt