Although it's perfectly natural to get annoyed by Windows' seemingly endless ‘New updates are available' alerts, it's not a good idea to ignore them. You do so at your own risk.
The vast majority of updates (which arrive on your system courtesy of the Windows Update tool) deal with security. Microsoft routinely patches newly discovered holes, adds malware definitions to its Windows Defender and Security Essentials utilities, bolsters Office security, and so on. And don't forget the occasional Windows hotfix, which may address serious issues such as random system lockups.
In other words, yes, it's absolutely necessary to update Windows. But it's not necessary for Windows to nag you about it every time.
Step by Step
Step 1. To make Windows Update work mostly behind the scenes, click Start, type
Windows Update, and press Enter. (In Windows XP, head to the Control Panel and seek out Windows Update.)
Step 2. Next, click the Change Settings option, and choose Install updates automatically. Click OK to finish the process. Now, the only time you'll hear from Windows Update is when it requires a reboot.
(For more solutions to perplexing PC problems, see "The 21 Greatest PC Mysteries--Solved!")