A Canadian Internet security firm is being credited in a joint effort to take down what is thought to be one of the world’s biggest botnets. Ottawa-based Defence Intelligence and Spain’s Panda Security assisted Spanish authorities in the dismantling of the so-called Mariposa network, which experts say consisted of 13 million computers worldwide. The network, which linked computers infected with a virus that stole personal information and credit cards, was first discovered by Defence Intelligence last May. In December, police successfully blocked the Mariopsa botnet, which included computers in 120 countries, more than half the world’s 1,000 largest companies and 40 major financial institutions. But it wasn’t until last month, after one of the alleged masterminds of the operation failed to disguise their computer IP address, that authorities were able to make several arrests in the case. Three Spaniards, ages 31, 30 and 25, are expected to appear before Spain’s National Court in Madrid.