[I lead Radar at Stripe] We're still investigating but have blocked the majority of this attack from the Stripe network. We're going to refund any impacted transactions and waive the fees for those payments. We'll also waive the dispute fee (if a payment has been disputed).

More broadly, we’ve seen an uptick in card testing attempts across Stripe. While the absolute rate of successful card testing across the Stripe network is flat-to-somewhat-down, it’s not evenly spread—some businesses are seeing more than others. For these new testing attacks, we’re deploying mitigants in real time.