Half of all Fortune 500 companies still contain computers infected with the DNSChanger Trojan, weeks after a FBI-led takedown operations targeting the botnet's command-and-control infrastructure.
DNSChanger changed an infected system's domain name system (DNS) resolution settings to point towards rogue servers that redirected legitimate searches and URLs to malicious websites, earning cybercrooks kickbacks from click-fraud scams and scareware distribution rackets in the process. The FBI stepped in and dismantled the botnet's command-and-control infrastructure in November.
The takedown operation – codenamed Operation Ghost Click – led to the arrest of six Estonian nationals, accused of manipulating millions of infected computers via DNSChanger. At its peak as many as four million machines were hijacked by the malware.
Rogue DNS servers were temporarily replaced by legitimate servers but nothing was done to disinfect pox-ridden PCs. That left organisations at a heightened risk of attack, not least because DNSChanger disables anti-virus software and security updates on infected machines.
A study by IID (Internet Identity), published on Thursday, found at least 250 of all Fortune 500 companies and 27 out of 55 major government entities had at least one computer or router on their network still infected with DNSChanger. The stats come data from IID's ActiveKnowledge Signals system as well as information from other leading security and Internet infrastructure outfits.
Darkness will fall
Barring further court actions, legitimate servers that were set up to replace rogue DNS servers will be deactivated on 8 March, 120 days after the initial takedown operation. Unless infected machines are fixed they will not be able to browse the web or send emails as normal after 8 March, once the plug is pulled on the replacement domain-name-to-IP-address-resolution servers upon which they currently rely.
Fortunately help is at hand through the ad-hoc DNSChanger Working Group and security firms such as Avira.
Avira has published a tool designed to allow users to see if their machines are infected with DNSChanger malware. The German firm, best known for its freebie security scanner software, has also released a free DNS-Repair tool so users can revert to the default settings of Windows with only a few clicks.
Sorin Mustaca of Avira explained the importance of taking action now, rather than waiting for possible problems to appear next month.
"If your computer was infected at some point in time and it was using one of the DNS servers which are now controlled by the FBI, after March 8, it will no longer be able to make any DNS requests through these servers," he said. "In layman’s terms, you will no longer be able to browse the web, read emails and do everything you usually do on internet. So, it is mandatory that the DNS settings of the computer are restored to their original state." More information on how to clean up infected machines before time runs out can be found at the DNS Changer Working Group website. ®