Only two countries have suffered significant DDoS attacks every single day for the past five months, and they’re probably exactly the countries you’d expect: China and the United States.

This interesting tidbit comes from Google’s new “Digital Attack Map,” a collaboration between the company’s Internet-themed think tank and the threat-monitoring service Arbor Networks. The data come with some disclaimers -- they don’t show every DDoS attack in the world, and it’s easy to fake the source of an attack -- but they still provide a fascinating glimpse of both the scale and the geography of cyberstrikes.

For the uninitiated, DDoS stands for Distributed Denial of Service -- it’s a common, relatively unsophisticated type of cyberattack that takes a Web site offline by overloading it with traffic from infected bots. Often when people say a Web site was “hacked,” they actually mean it suffered a DDoS attack. Verisign estimates that a third of downtime incidents stem from DDoS attacks -- and, perhaps more alarmingly, that two-thirds of large and medium-size American businesses suffered an attack in 2010.

That’s a big deal, because DDoS attacks are extremely costly for both businesses and consumers, and they’re only becoming costlier. An April report from the security firm Prolexic found that attacks became bigger and more frequent in the first three months of 2013. DDoS is also a favorite tactic for shutting up media organizations and government agencies the attacker doesn’t like -- see the many, many DDoS's by groups such as Anonymous and the Syrian Electronic Army.

So why are the United States and China such popular targets? It helps that there’s so much to target -- those two countries have more Internet users than any other by a pretty decent margin. Both are also popular choices for ideologically based attacks.