Changing your port isn't going to help as I assume the hackers can easily scan all ports on your router.
FYI - you may want to check out Shodan. It is kind of a search engine for finding out specific information on ports and services available on the internet, including your router, assuming that you are attached to the internet. Shodan reports over 18,000 hits for Blue Iris - in other words it has found 18,000 IP addresses that have the Blue Iris server running. 12,800 of those are using port 81, the rest are using other similar ports like 80, 8080, 8081. You can narrow down searches using various criteria - here is a search that returns all BlueIris connected devices in Chicago: Shodan
Note - you may have to create an account with Shodan to do searches but it is free.
FYI - you may want to check out Shodan. It is kind of a search engine for finding out specific information on ports and services available on the internet, including your router, assuming that you are attached to the internet. Shodan reports over 18,000 hits for Blue Iris - in other words it has found 18,000 IP addresses that have the Blue Iris server running. 12,800 of those are using port 81, the rest are using other similar ports like 80, 8080, 8081. You can narrow down searches using various criteria - here is a search that returns all BlueIris connected devices in Chicago: Shodan
Note - you may have to create an account with Shodan to do searches but it is free.