I feel that other people use my computer from the outside without my permission. How do we know?

Question

I feel that other people use my computer from the outside without my permission. How do we know?
Thanks for your help

Answer 1

First thing to do is find the information you received on your internet service, which should have the info on logging in to your router itself.  Login, usually from a browser like Safari, and find where to change the admin password, not the netowrk or WiFi password.  Change the admin password from the factory default, and write it down so you don't forget it...if there is ever a problem with your service you have to have that.
Once the router is secure, on your iMac how do you operate?  Did you just set it up out-of-the box without adding user accounts?
With the router secure there is little risk of an intruder using your equipment...but it would be worth it to change your network password, especially the wireless part of the network, and to check to see what security method is being used.  The most secure is WPA2.