Cyber attacks with enough firepower to knock entire countries off the Internet have spiked in recent months, raising fresh concerns within the security community about weaknesses in the Internet infrastructure that help create such weapons of mass disruption. These “distributed denial of service” or DDoS attacks use robot networks or “botnets” — many hundreds or thousands of compromised PCs — to flood targets with so much junk traffic that they can no longer accommodate legitimate visitors. While DDoS attacks have been a common threat since the dawn of the commercial Internet, DDoS watchers, such as Arbor Networks, have tracked a recent spike in the number, sophistication and size of attacks against major Internet providers. Attackers also appear to be picking bigger targets.