What is the causes computer and account tampering with all security measures in place. What steps am I missing?

No one in my houshold tampers with computers or causes malicious problems.

What is the cause of malicious tampering and email theft when all system preferences show all users and sharing options removed, all security and password options changed, firmware password installed, location options removed, iCloud not set up, accessibility options turned off, contacts/calendar/reminders not used, remote and keyboard options turned off, bluetooth not in use, internet accounts removed, WiFi/Router updated with WEP/WEP2, etc.

These changes cut down on problems but some still occur. I found that erasing the system completely back to factory helped. Even though it was done twice within a few months, problems still get back on the computer and IP Address searches only show my IP Address.

I changed to direct Ethernet with no WiFi use to see if this makes a difference. So far there have been some issues and the wifi will still get turned on. I have to check periodically to make sure it is turned off.

Yet the computer is still accessed from some other sources, the guest account is turned on, some keyboard shortcuts are activated, the WiFi is turned on.

Logged onto the computer one day and found the Terminal opened on the desktop. Since I don't know how it works, I could not figure out what happened.

Email was used by someone else and only my IP Address showed on history.

Documents, computer options, Safari, email, passwords, software, iTunes & Apple App Store, etc have issues including getting changed or damaged.

IxQuick is used as much as possible to reduce spying but noticed that more Safari pages are giving messages saying it can't be used to open websites. Also the right click option to open pages in a new tab has a reversed order from yesterday. The choice to open in a tab was first, then windows 2nd. Today windows is first and tabs are 2nd. I assumed the order was standard and did not change.

Sophos and other mac security was installed via downloads and/or disks, but were shortely dismantled or could not perform due to errors.

External back up systems, both cloud service and HD, were full of errors or not working after a few days to few weeks. New servicings and HD were purchased but they too were not working in a short period.

Will the Console show all activity?

New email accounts are attacked as soon as they are opened with all the recommended security measures in place. Email history is blocked and erased. Only my IP Address shows as access. Emails and documents are stolen. Notificaitons are blocked and grayed out so it can't be turned on. Passwords are changed. Emails are sent to people I don't know with no history of the email details. Email technicians don't seem to be aware of the causes of such things and some had admitted enough information was stolen for ID Theft. With all personal information known a person can get into future accounts. btw-which email services, paid or free, are better and more sucure?

How is this happening. What am I missing? What needs to be fixed, changed, or installed?

How to gurantee iMac security?

Where to look for foreign prgrams or items installed in the computer?

How can the computer IP Address be changed?