If so (and if you’re running Windows), it’s because of another out of band (i.e. not falling on a Patch Tuesday) security update release for Internet Explorer.
Summary of the patches released last night is in the bulletin.
If your computer didn’t reboot, or if you’re not certain if you got the patch, you definitely want to install it now (including if you’re running IE 8 on Win 7). The threat is remote code execution (more info in that particular threat is here).