What exactly is this? I just did an update...
I just updated, and it asked me to restart. When I got back on this popped up...
MacBook Pro, OS X Mavericks (10.9)
That is an addon for Safari. You can click on uninstall to remove it, or slide the on tab to the off position to temporarily disable it.
Some extensions are harmless like Duckduckgo that enable searching just by Duckduckgo from the search field. Others can be more notorious if you don't know what they are for.