At around 5pm PST on 12/5/14 we noticed a degradation of our service. We called in the issue to our hosting provider Rackspace who confirmed that the network section that our load balancer is located on was under a Denial of Service (DOS) attack. Rackspace was able to fix the issue at 6.30pm PST. The unfortunate result is that our tracking would not have worked during that time frame, including sending data to Google Analytics. Since our code is loaded asynchronously, users should have been able to continue using and placing orders on stores.
I should also mention that if you have noticed a higher than usual percentage of missing transactions (>5%) in Google Analytics in the past two weeks, this is a separate issue. Yahoo! tech support has confirmed that under some circumstances the order status instead of the order confirmation page would load when an order has been placed. In that case no order information would be sent to Google Analytics.
I am really sorry about this issue.