To stay protected, the International Maritime Organization (IMO) recommends that vessels introduce cyber security plans no later than the first annual renewal of the company ISM Document of Compliance after 1 January 2021.
The Guide's five functions are:
#1 Identify: Which systems are the vulnerable ones, which systems are vital to operations and who is responsible for them.
#2 Protect: The plan should define measures to prevent attacks from occurring.
#3 Detect: If an attack happens, recognize it quickly and mitigate the damage.
#4 Respond: Plan a clear means of getting back up and running as quickly as possible using a second system.
#5 Recover: Get the primary system back running and analyze the cause.
Concluding, to learn more see the interactive guide here.