While Windows 10 Insider Preview build 18305 was only released to the Fast ring yesterday, Microsoft is releasing a cumulative update for the build, which has an Internet Explorer security fix.
Build 18305 RSS
Build 18305 was released today for Insiders in the Fast Ring, bringing features such as Windows Sandbox, password-less account setup, and more. There are some known issues to be aware of, though.
Microsoft released Windows 10 Insider Preview build 18305 today, with a ton of new features. These include things like Windows Sandbox, the new Office app, Start Menu changes, and quite a bit more.
Microsoft is working on Windows Sandbox, which is a lightweight virtual desktop environment integrated in Windows 10 that allows you to test potentially harmful applications in a sandbox.