Telstra has attributed a "router issue" in the United States to the degraded web browsing experienced by some cable and ADSL users in the past three days.
Users have flooded the Whirlpool forums and social networking siteTwitter, complaining that they were unable to access large US sites such as Facebook and that online gaming was also degraded.
Sources told iTnews that there had been three incidents of degradation since Monday night, each lasting approximately two hours.
The issues were thought to have affected between 15 and 20 percent of internet traffic from the US to Australia, although this figure could not be confirmed with Telstra.
A Telstra ISP representative had earlier posted to Whirlpool that the issue was related to the undersea cable network operated by Reach, some of whose assets fall under Telstra International.
"We've been working with our partners in Reach on this," the Martin@Telstra account posted.
"The Reach engineers did become aware of an intermittent issue that appears to be coming from some other partners of theirs in the US."
A spokesman for Telstra has told iTnews that "some customers intermittently may have experienced slower than normal internet speeds in the past 36 hours when accessing international websites... due to a router issue in the United States".
"We have implemented some changes and are monitoring the service to confirm it is resolved," the spokesman said.
"We apologise for any inconvenience during this time."