The company says some transactions were being processed, but numerous Worldpay merchants reported significantly lower sales since the inset of the attack. The service says it has 30,000 clients in 70 countries around thew world, including Vodafone and Sony Music Entertainment.

The attack on Worldpay follows similar attacks on Authorize.net and several smaller payment processing services. In each of those cases, the attack was preceded by a demand for payment.

The attacks are an additional challenge for an industry experiencing turbulence and consolidation, as several payment processing companies are closing or being sold. The cost of these attacks is felt not only in lost sales, but also in costs to implement sturdier digital defenses against DDoS blackmail schemes, which have also been a significant problem for online betting services.

DDoS attacks are a particularly potent weapon against sites with limited resources to defend their sites or pay overusage fees from attack-related bandwidth consumption. But with more attackers using large botnets of compromised computers to mount attacks, recent DDoSes demonstrate that even large corporate providers can find their web infrastructures hobbled by extortionists.