Domain hijacking is where an unauthorized person is able to gain control over your domain. The most common cause of hijacking is caused by weak security. Most often, a hijacked domain will suddenly point to a different website.
You can monitor for this by using record triggers. They check on an hourly basis for changes in records, and when those deviate from the expected result, they will raise an alert so you can immediately handle it, even before your customers notice.
For .com, .net and .org TLDs it is also possible to enable the “Transfer Lock” setting in your domain settings. It can be used as a reminder if the transfer lock is disabled for your domain. It can also send alerts to remind you.
You can find more on record triggers and how to set these up on the following article.