Security update for Bing toolbar?

Windows Update is offering an important "Update for Microsoft Silverlight (KB2416427)" and says it "improves security, reliability, accessibility support, startup performance, etc." There's a helpful link to find out more information which takes you to the cited KB2416427 article.

But the article merely says "This update fixes an incompatibility issue between Microsoft Silverlight 4 GDR 1 (4.0.50826.0) and earlier versions of the Bing Toolbar." I didn't even know there was a Bing Toolbar.

But, really, don't the people at Microsoft talk to each other? Is the KB article just woefully inadequate or is Windows Update lying? Either alternative still undermines confidence in Microsoft security updates.