If you're using Internet Explorer 11 on Windows 7, read this!
Microsoft has decided not to give you any new IE 11 security updates unless you install the patch it released on April 8. The patch number is KB2929437. You can check your Windows Update patch list to see if it's installed.
If you have Windows set to auto-update, then it shouldn't be a problem. However, I do know that some people like to pick and choose what patches to install, and therefore you might have missed it.
You can install the patch from Windows Update or download and install it manually from Microsoft's website. Note that this download has a number of patches in it.
Once the patch is installed, go back to Windows Update and make sure the latest Internet security update is installed. This group of patches fixes some serious problems that could allow hackers to take over your computer remotely.