In this age of electronic attacks, it makes sense to ensure that your PC is as up-to-date as possible with the latest security updates. Fortunately, the two major vendors of OSs, Microsoft and Apple, as well as most Linux distributions, provide ways in their systems to automatically download and, in the case of Microsoft, even automatically install the most critical updates.
Microsoft has provided the Windows Update service for years, but the latest version, called Microsoft Update, is even better because it alsoprovides updates for a number of non-OS applications, including Microsoft Office. But Microsoft's Automatic Updates service is perhaps the company's best security-patch tool for individuals. By setting this feature correctly, you can configure your system to automatically download and even install any critical security patches. Yes, there have been a few problems with Microsoft downloads over the past year, but the alternative—such as an Eastern European hacker gaining remote access to your PC—is arguably a worse fate than having to reinstall the occasional buggy patch.
On the Mac, Apple provides the Software Update service, which launches automatically whenever a patch is available. This service can't automatically download patches, but it will at least warn you when an update is available.
Various Linux distributions handle software updating differently, so check with your OS vendor for details. The popular Ubuntu distribution includes a new Software Updates applet that works a lot like Apple's Software Update: When security fixes and other updates are available, a yellow balloon window pops up in the upper right corner of the screen, letting you see what's new.