Your browser is out of date, Time to update to Internet Explorer 11, Your Java software needs updating, your media player needs an upgrade, or many other, similar messages.
Lots of times these are fake offers that, when installed, will cause LOTS of new popups on your computer and, because you said yes to all of the installations your antivirus couldn't even help.
Almost all legitimate upgrades notify you by a popup by your clock. If you see any other upgrade, and you think you may need it, go directly to the manufacturer's website to get it.
Only get Internet Explorer from Microsoft.com
Only get Java from Java.com - Only get Flash from Adobe.com