The BBC has revealed that TalkTalk's net filtering system, which blocks millions of web addresses and has been praised by Prime Minister David Cameron, is being controlled by Chinese networking giant Huawei.
Huawei has come under scrutiny in recent months after being blocked from doing business with the US after allegations that it has links to the People's Liberation Army in China and that ultimately any Chinese company is subject to the Chinese government.
It has a 10 year relationship with BT where it provides equipment for much of the UK's critical national infrastructure. However, news that it is also responsible for monitoring and controlling access to content for UK citizens will likely raise further concerns.
David Cameron unveiled plans this week that will see internet service providers (ISPs) block pornography by default, where consumers will soon have to opt-in if they wish to view pornographic content. On Monday he said that TalkTalk had shown "great leadership" in setting up its system, Homesafe, which it has offered to customers since 2011.
Homesafe is a voluntary scheme, but customers of TalkTalk that don't want filtering still have their traffic filtered through Huawei's system, but matches to the database are dismissed rather than acted upon, according to the BBC.
Huawei reportedly has a blacklist of over 65 million web addresses and denies access if there is a match. The content of the list is collated via an automated process, but both Huawei and TalkTalk employees are also able to add and remove sites independently.
Concerns have been raised as to whether private companies should be given the power to decide what content should be blocked, but Cameron has said that the actions of the ISPs will be monitored.
However, questions are likely to be asked about whether Huawei, a company that has had a number of security concerns raised against it, should have such control.
The Intelligence and Security Committee (ISC) recently said that they were "shocked" that officials at BT had chosen not to inform, let alone consult, ministers on their decision to purchase equipment from Huawei, which could pose a risk to the UK's critical national infrastructure.
An ISC report said: "The difficult of balancing economic competitiveness and national security seems to have resulted in a stalemate [and] given what is at stake, that is unacceptable."
However, the government has since released a statement that largely dismissed the ISC's concerns and stated that it does not agree that national security issues are overlooked.
David Cameron has also accepted a £1.3 billion investment from Huawei up until 2017 in research, development, centres of excellence and procurement.
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