How do I know if I can trust an internet update?

[Mark]

You didn't say WHAT it "needs to update". If it's Microsoft Windows, it'll pop up in the toolbar.

HOWEVER, if an Internet Explorer page is opening up and saying that Windows needs to be updated... then that's due to a bad ad trying to trick you into downloading malware.

Make sure you have a good antivirus program that's up to date, and scan your computer. Also, scan your computer with Malware Bytes (http://www.lavasoft.com ).

If all three programs report your computer is clean, then the most likely source (in my experience) are Adobe products (like Adobe Flash or Adobe Reader), your printer software, or a program like NVidia Experience (which notifies you about new drivers).

If you're STILL not sure if the update is legit or not, try installing Belarc Advisor. It'll scan the programs you have installed and notify you of updates.