Your computer has many applications that need updating in addition to your Operating System (OS) updates. This can include PDF viewers (Adobe Acrobat), browsers (Firefox, Safari), and others. Any of these applications could have security issues and require updates.
Unfortunately, there is no one place to go to update all of your applications. The good news is that many applications are now automatically notifying users of updates. For other programs, you can check the vendor’s website periodically.
Your web browser relies on numerous software plugins (also called extensions or add-ons) to display content such as video, audio, or office documents. Those plugins are frequently vulnerable to attack and are easily exploited by so-called "drive-by browsing attacks," in which merely browsing to a website can lead directly to a system compromise.
For Internet Explorer, just click Tools>Windows Update and follow the prompts. You must repeat this process until it comes back with no more updates needed.
For Mozilla Firefox go to this link https://support.mozilla.org/en-US/kb/update-firefox-latest-version
Google Chrome automatically notifies the user, so no special action is needed.
Apple Safari automatically notifies the user as well so no special action is needed.