A largely prevalent malware campaign that dropped a Trojan during the recent years has been the DNSChanger campaign, which involved altering the configurations of the Domain Name System server associated with infected PCs so traffic maybe redirected onto harmful servers, published Cnet on January 23, 2012.
It maybe noted that DNSChanger represents certain group of malware programs, which changes the network settings on computers running Apple's Mac OS X or Microsoft's Windows such that when the queries related to DNS is created to be sent to the servers of the end-users' ISP, they get diverted onto the online-crooks' servers, instead. These latter malevolent servers subsequently issue fake replies so the end-users would encounter PUP (potentially unwanted programs). Indeed starting 2007, security researchers observed the Trojan as also the rogue DNS servers in their active form.
Moreover, they caused the number of infected PCs to grow to 4m, including approximately 500,000 situated inside the USA. The criminals tampered with the local PC's DNS for diverting end-users onto unintended websites alternatively for posting their own malverts in place of the actual page contents.
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