The addressbook on your PC? Or an addressbook you might have with an online account, such as Gmail? If someone has access to your PC's addressbook, that means they have access to your PC and are running software on your PC. Your bigger problem is in getting them off the PC. Check your antivirus and firewall settings, and possibly have an expert check the PC for malware.

Hi David ... I went into my contacts on my AOL account and added a contact 000000 first and last name. I am hoping that will stop it. Thank you so much for your response ... I have Norton everything so don't think they accessed anything but my email.

That 'sounds like' they just accessed the online AOL addressbook, not the PC itself. Still, that indicates the person may have access to your AOL account, so a change in password may be needed - which would then entail changing the password on Thunderbird.

Yes indeed already done !!! THANK YOU SO MUCH FOR YOUR TIME !!!

You are very welcome. I was glad to assist. :)