Running a WordPress site (like this site)? Make sure you update to WordPress 4.7.3 (like this site.) According to WordPress, the update fixes six important security bugs, including three cross-site scripting bugs that could allow hostile code to run on your WordPress site. The update also includes 39 regular maintenance releases. If you have automatic updates enabled (like this site) then you have probably been updated. If not, you want to go to your dashboard and do a manual update.
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See the WordPress support bulletin for more details on the bugs, and credit to the people who reported them.