Gangs of phishers are stepping up their abuse of specific top-level domains, according to a survey by the Anti-Phishing Working Group.
The study, "Global Phishing Survey: Domain Name Use and Trends in 1H2008," (PDF) which covers the first half of 2008, surveyed 47,324 unique phishing sites located on 26,678 unique domain names. The researchers found the number of TLDs (top-level domains) used by phishers for their attacks grew 7 percent, from 145 in the second half of 2007 to 155 in the first half of 2008.
As part of judging the pervasiveness of phishing among TLDs, the authors measured the number of phishing attacks per 10,000 domains. The top two TLDs in this category were .hk (Hong Kong), which led with 142.1 phishing attacks per 10,000 domains, and .th (Thailand), which came in second with 43.1.
The authors found that .su (Soviet Union), .ru (Russia) and .fr (France), ranked third, fifth and tenth respectively, received high scores in this category because phishers launched large numbers of attacks in these TLDs via subdomain hosting services.
"The widespread use of subdomain registration services by phishers is a challenging development for the industry," Rod Rasmussen, co-chair of the APWG's Internet Policy Committee, said in a statement. "These services have diverse business models and controls, and run outside the scope of ICANN [Internet Corporation for Assigned Names and Numbers], domain registries or any recognized authority. This can make them an unwitting haven for phishers and in turn adversely affect the reputation of a TLD or registrar who has no control over their behavior."
The study also measured the number of phishing domains per 10,000 registered domains in that TLD. In the case of .com, there was an average of 1.6 phishing domains per 10,000, putting it at No. 71 among TLDs in that category. The .hk domain was again first with 32.2 per 10,000.
According to the study, 4,512 subdomain sites or accounts were used for phishing under 274 unique second-level domains. These were established on subdomain registration services where customers set up a subdomain under a secondary-level domain owned by the service provider.
The proportion of IP number-based phishing sites decreased 35 percent in the same period, dropping from 18 percent in the second half of 2007 to 13 percent in the first half of 2008.
"We're seeing a trend away from fixed IP-based URLs which are readily shut down to use of more domain-based URLs," Rasmussen explained. "Many of these are on compromised servers which already have established 'good' reputations, while others are on fraudulently registered domain names supported by botnets or other throw-away hosting resources."
He added, "In either case, the mitigation effort is challenged, as one does not want to suspend an innocent domain name, while with a botnet, the domain is the only practical choke-point to neutralize the attack."