A Telstra spokesperson said the carrier had narrowed the list of malware that could have infected the computers to three, adding the problem could have been caused by a combination of those viruses or Trojans. He declined to name the suspects.
He said the PCs generated 95 percent of the bogus requests which caused the problems that evening.
The spokesperson said the carrier was planning to implement additional technologies to protect its DNS systems against malware.
The carrier had ensured the PCs were disconnected once identified and was "working with those customers to ensure the problems do not happen again".
BigPond said in its original statement outlining the problems it "strongly recommends its customers install and maintain adequate security measures on their PC to avoid virus and Trojan infections and the subsequent impact they can have on other Internet users".