It had to happen sometime. After steady growth in internet bidding, Christie’s finally made a big score online today when a bidder won Edward Hopper’s October on Cape Cod, the star lot in today’s American Art auction, for $9.6m or a hammer price slightly above the $8m low estimate.

Christie’s says “for the year 2011, 29% of Christie’s bidders transacted online, and the LIVE™ platform drew 25% more bids than the previous year.” We’re not entirely sure what “transacted” means here. Let’s assume that they’re saying nearly a third of all bidders have placed an online bid.

All that’s important today is that a buyer was confident enough with the online bidding system to conduct a very substantial transaction online. Whether the buyer was bidding in the room from a smartphone or sitting at home or in the office placing bids, we’ll never know. But trusting a nearly $10m transaction to the internet is a significant milestone.