Hi JDMAC1,
Thank you for reaching out to us in our community and welcome, we are sorry to hear your Father- In-Law is having issues with Netflix Via the box even though OK when signing in via your phone, we would need to have a look however as it is an Online account issue this is only something we can help the account holder with, are you able to call us when with him so we can help with all the below, if he belies he has been hacked the first thing is to change the Online Account password, select forgotten username and password first then answer the additional questions then change the password to something totally different to previously used.
Then un a virus scan on all devices used to log into his emails, you can find out more around this here.
Regards
Paul.