According to the release announcement, Chrome 71.0.3578.80 addresses forty-three distinct security vulnerabilities in earlier versions of the browser.
The full change log for the new version has over twelve thousand entries, none of which are mentioned in the announcement. Many of the changes appear to be fixes for minor bugs.
To check your version of Chrome, click its menu button and navigate to
About Google Chrome. If you’re not running the latest version, you’ll be able to update it from there.