Shopify/active_merchant — pull request #1236 by mnoack (2014-06-02 07:31:07+00:00)
Title: Verify the length/format of the card verification value

I've made this PR as customers on our website are getting an error because they are typing their credit card wrong.

I noticed ActiveMerchant doesn't yet validate the card verification value but does validate everything else and it makes sense to validate this field as well, however I do acknowledge it's changing the core of the system (not just adding/tweaking an individual gateway) so I'm open for suggestions.