It's not a flash update, it's malware

No, you don't need to update flash. Two of my friends with Macs have ended up with malware on their computers recently and I think the vector is agreeing to install what pretends to be a Flash update. I've seen a few of these recently and I think they're coming in via targeted ads that re-direct multiple times before showing things like this.

Just close the window. Here's a few more examples.