Essentially, a number of Google IP addresses were advertised as free for internet traffic, and thus had traffic routed to them by local and foreign service providers, so long as the traffic was meant for Japan.
The problem stemmed from the border gateway protocol (BGP) - a cooperative system that networks together smaller networks to make up the internet. But BGP's shortcoming is that it's up to network administrators to check and filter information in route advertisements.
Online banking, railway payment systems as well as gaming sites were among those affected.
At the end of last week (via TNW), Google mistakenly set network information incorrectly which led to traffic being directed through Google instead of ISPs. In total, NTT provides Internet services to 7.67 million home users and 480,000 companies. The issue is now under investigation not only by Google, but by the Internal Affairs and Communications Ministry of Japan.
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It is unknown if the BGP route hijack was the result of a human error or an equipment malfunction. We modified the information to the correct one within eight minutes. NTT Communications was hit the hardest by the ordeal, having its traffic jump on 24,834 Google ports.
BGPmon, an industry recognised expert in network monitoring and routing security, said over the weekend that more than 135,000 prefixes on the Google-Verizon route had been accidentally announced, causing the disruption. "We apologize for causing inconvenience and anxieties", the spokesperson told The Asahi Shimbun.
"In this case it appears a configuration error or software problem in Google's network led to inadvertently announcing thousands of prefixes to Verizon, who in turn propagated the leak to many of its peers", he added. "At the minimum Verizon should probably have a maximum-prefix limit on their side and perhaps some as-path filters which would have prevented the wide spread impact".