The irritating feature of the popups is that they don't tell you anything about what new programs it's talking about. It would be useful to know that Adobe, or Microsoft, or Sun, or Symantec had done something, and it was not AbdulInNigeria or ChungYangYung from N Korea messing with you.

Some updates ask for permission to download an update and others may download them automatically.

Downloading is a separate operation from installing an update.

Some downloads install automatically, but for others you must provide a separate permission to install.

Some update installations require a reboot in order to complete and "turn on" the installation. Occasionally an update installation will do what it can and wait until you reboot to turn itself on. Others will ask permission to reboot. Some reboot automatically without asking (which is rather rude IMO). Some will reboot without asking the next time the computer is "idle" and the installer thinks you won't notice.

Since there can be multiple steps in an "installation," the popup can (assuming profound stupidity on the part of the programmer) signal an "installation" when it merely means that "the next step has been completed."

It's also quite possible that another program has installed an update without asking permission and without informing you while your computer was idling.

In Windows (which we know you use only because you mentioned clicking the Start button) Control Panel, at the Add/Remove Programs (or whatever it's called in your version) you should find a "click" to "Show Updates" that well reveal most recent "updates." The Windows updates should be complete, but some third-party program updates sometimes don't show up there. You may be able to find, by checking date/time info, what's prompted the popup in a specific case, if you care enough to look; but Microsoft assumes you must be an idiot or you wouldn't be using Windows, so they may neglect to show you anything "you don't really need to know."

John