Hello this is me,
ZenKey looks to be a Multi factor Authentication service, similar to Yubikey. If you are unsure of how it got installed on your computer then you should remove it.
Regarding your Yahoo account have you attempted resetting the password? Click or tap here to begin the process.
Please note regarding Yahoo and AT&T – Beginning mid-November 2017, you will no longer be able to sign in to myAT&T or att.net with your Yahoo ID. Beginning early December 2017, all merged email accounts will be separated into two separate email accounts.