You don't need to switch the millions of cards nor the whole POS infrastucture to do changes for online purchases - things like http://en.wikipedia.org/wiki/3-D_Secure cover it fairly enough, I believe - it will deny online purchases with stolen CC data or a physically stolen card or both-sides-photographed, copying all the visible data including the cvv code.
You don't need to switch the millions of cards nor the whole POS infrastucture to do changes for online purchases - things like http://en.wikipedia.org/wiki/3-D_Secure cover it fairly enough, I believe - it will deny online purchases with stolen CC data or a physically stolen card or both-sides-photographed, copying all the visible data including the cvv code.