Internet, What's up with 'Java Runtime Environment' update?

The box recently pops up on my screen when I get online or shortly thereafter. It stops the screen and gives me only the choice to download now or ask later (sometimes it doesn't even say ask later).
If I click 'ok' my computer says…'Java Runtime Environment is not normally downloaded and could harm this computer! Click 'cancel' now.
I have 'Java' among my programs since 2009, but have no idea what it does.
P.S. The 'Microsoft' logo appears behind the 'Java download now' box but can't be accessed.
Explanations please?
A scam?
When my computer refuses for safety issues I get concerned.

To update Java, uninstall the installed version(s), then visit the official site http://www.java.com/...va.com/en/ and click the Download button.

An alternative is to run the offline installer, available from the the Java developer's website.

http://www.oracle.com/...33155.html

In most cases, you'll want the Windows x86 Offline If you play Minecraft and run Windows 64-bit, download the Windows x64 (exe version, 88.37 MB) installer.

It's possible that you don't even need Java, so after uninstalling, you might want to delay reinstalling to determine whether anything on your computer or the sites you frequent actually require the program.