Attacks exceeded 100 Gbps multiple times in the first quarter of 2013, Prolexic said, adding that the campaigns it is seeing appear to be coordinated and from skilled attackers. The firm said it mitigated an attack that exceeded 160 Gbps. More than 10 percent of attacks now exceed the 60-Gbps threshold, the company said. Vulnerabilities in unpatched web servers are fueling many of the biggest attacks, according to Prolexic's analysis. "Attacks that have generated the highest bandwidth and packets-per-second volume against our infrastructure have been targeted attacks from infected web servers with use-level permissions," Prolexic said.