Originally scheduled for release next month on February 15, 2018, Ubuntu 16.04.4 LTS is the fourth of five scheduled maintenance updates for Xenial Xerus, and it was supposed to ship with up-to-date kernel and graphics stacks based on those from the last stable release, Ubuntu 17.10 (Artful Aardvark). As you may be aware, two severe bugs were unearthed earlier this month, Spectre and Meltdown, discovered to affect billions of devices powered by modern processors. The industry has been working to mitigate these security vulnerabilities, but they’re not so easy to fix, so Canonical decided to postpone the release of Ubuntu 16.04.4 LTS to include kernel mitigations for these bugs.