Apple released a security update to 10.13.4 today. I have installed it and it took about 25 minutes. It updates the Safari web browser as well. Apparently, the security update fixes vulnerabilities to “LinkPresentation”. Here is an official description of what this update does:
According to Apple’s release notes, Security Update 2018-001 is recommended for all users and is meant to improve the security of macOS. The update addresses two security vulnerabilities related to Crash Reporter and LinkPresentation, both of which could be used maliciously to gain access to a Mac. A Safari 11.1 update is also included, with fixes for WebKit vulnerabilities.
As I said, I have installed it and there are nt problems as far as I can discern. Any kind of security fix to macOS is a must install as afar as I am concerned, especially if it involves Safari and online activity.