CSO's ]

To prevent a disruption of victims' Internet service, ISPs redirected traffic to keep customers online. The companies also notified victims via mail and email with instructions on how to remove the malware.

While ISPs were given kudos for helping avert what could have grown to a major problem, they were also criticized for choosing to redirect traffic, instead of insisting that customers clean their systems of malware.

"We can't keep providing a safety net for people with malware-infected computers on the Internet," Chester Wisniewski, senior security adviser for Sophos, said on Tuesday.

Rather than wait for a crisis, ISPs should continuously monitor for malware in customers' computers and take infected systems offline until they are cleaned, Wisniewski said. In the case of DNSChanger, computers that had their traffic redirected remained infected, and could be carrying other viruses.