That's not quite surprising. Online and hot wallets are one of the most vulnerable wallets in the market. And this exploit, though clever, should be pinned down. A seemingly harmless bitcoin address generator could steal your precious bitcoins in an instant. It's a good read and warning for newcomers. Storing bitcoin should be treated as a real asset, that is, to carefully store and manage your bitcoins. Cold storage and hardware wallets are still more secured than these hot wallets.