Last week, the WordPress project issued an update that had a flaw in
it. It was caught almost immediately and within a few hours a patch was
released. As WordPress states in their blog, the 4.9.3 release of WordPress “will cause sites that support automatic background updates to fail to update automatically, and will require action from you for it to be updated to 4.9.4.”

Why is the 4.9.4 release so important? Updating to 4.9.4 is
important, because it allows your site to get automatic security
updates without any intervention from you. If you do not take action and
update your site to 4.9.4, when new security patches are released, your
site will remain vulnerable.