If you're running Windows Vista or Windows 7, there's a fairly nasty exploit running around related to the sidebar. Microsoft isn't even releasing a patch for it. Their fix is to just disable the sidebar completely. That functionality is being discontinued in Windows 8, which most likely factors into Microsoft's approach to this.
Microsoft has released a "Fix It Tool" that will disable the sidebar for you. Simply click on the applicable link to download the "enable" or "disable" installer (MSI file), and then run it. If you are responsible for multiple PCs, you can download the MSI file, put it on a USB drive or CD, and install it from there. It does NOT require an active internet connection to install.
I've already applied this on my work PC, and will be applying it on my home PCs this evening.
I'm not real thrilled about having to disable the sidebar. I've really liked some of the sidebar gadgets, like weather and calendar and Google and the like.
Also, I have no idea if this exploit applies to the Google sidebar, if you have that installed. As best I know, it only applies to the Windows sidebar. I also don't know if disabling the Windows sidebar has any impact on the Google one or not. I'm sure I'll find that out this evening, as I believe I'm running the Google sidebar on at least one machine.