An IT technician has implemented a major security upgrade to an organization's accounting system software. After the upgrade, none of the authorized users can launch the app. Each attempt of running the app results in a message indicating "this app is blocked, please contact your system administrator". Which of the following did the technician most likely overlook?

a$.$

Allow lists$/$deny lists

b$.$

Downtime

c$.$

Legacy applications

d$.$

Application restart