Q:What the heck is Microsoft Silverlight?My Windows systems keep trying to install it on updates, and I’ve opted not to on two of my computers. Is it a necessary piece of add-on for home user Web browsing (similar to Java or Flash) or just another piece of bloatware?

—W. M., Raleigh, N. C.

A: Microsoft Silverlight is indeed a Web browser add-on similar to Flash or Java, said Paul Rosenberg, owner of Love Your Computer, a repair shop in Chapel Hill, N. C.

While new and not as widely used as those two add-ons, Silverlight will not slow your system down or load it with unnecessary content, and therefore would not be considered “bloatware,” he said.

For its part, Microsoft calls Silverlight a “powerful development platform for creating rich media applications and business applications for the Web, desktop and mobile devices.”

You can find out more at www.microsoft.com/silverlight/ what-is-silverlight/.

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Q: My hard drive is getting full, so I am trying to remove unnecessary programs. The programs are listed in Add/Remove Programs in the Control Panel, and when I try to remove them, I get the message, “This action is only valid for products that are currently installed.” I know the programs are installed because I can open them and run them from the start menu. How can I remove these programs? I installed Windows Cleanup and tried to remove them that way and I think that might be why I can’t remove them from Add/Remove Programs.

—P. R., Miami

A: It is very likely that trying to remove programs with Windows Cleanup is the reason you cannot uninstall them properly now, Rosenberg said.

Windows Cleanup, a free program that promises to delete temporary files and remove unneeded registry entries from your system, probably has removed the installation records for your applications, he said.

So while Windows can still run the applications, it no longer has the correct instructions for uninstalling them. Your best course of action would be to reinstall the applications in question, then uninstall them using “Add/Remove Programs” under “Control Panel,” or “Programs and Features” if you are using Vista or Windows 7, Rosenberg said.

In the future, he advises you to always use the control panel option for uninstalling applications, and he recommends great caution in using any utility that claims to clean up your registry, as it is too easy to make a mistake like this. “In fact, I see no reason to ever let any utility modify your registry at all, unless you are in a mal-ware removal situation,” he said.