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The move comes months after Prime Minister David Cameron started a campaign to fight against porn and other sensitive content that could be harmful for children.

"New customers will have to make a choice on whether or not to activate the parental controls when setting up their Internet connection for the first time," BT wrote in a press release. "The option of having the controls implemented is pre-selected and customers have to confirm that choice or actively choose not to switch on the controls which block content potentially unsuitable for children."

And what about the almost 7 million existing BT users? In 2014, they will receive a somewhat awkward request from BT, asking them if they want to set up the same filtering controls — basically asking whether they'd like to be able to access porn sites or not.

The well-intentioned program, championed by Cameron, has received a fair amount of criticism.The Daily Beast called it "idiotic."

Further incensing critics, Cameron also praised major ISP TalkTalk's filtering system which, it turned out,was developed in partnership with Chinese network company Huawei. The U.S. and UK governments have repeatedly accused that company of spying on its customers on behalf of the Chinese government.

All six major UK providers have agreed to apply Cameron's porn filters by default. TalkTalk and Sky are already asking their customers if they want to turn them off when they set up their home broadband connection, and Virgin Media is expected to follow suit soon. Together, these four providers have more than 20 million subscribers, or 95% of all UK home broadband connections.

BT's filtering system will have three levels: strict, moderate and light. In addition to sites containing pornography, illegal drugs and those that promote suicide, the filters can block less pernicious content such as nudity, social networking, and gaming, as reported by the BBC.

In August, several UK ISPs told Internet freedom advocates at the Open Rights Group that the system will end up censoring way more than just porn.

"David Cameron wants people to sleepwalk into censorship," Open Rights Group's Jim Killock wrote at the time.

"Internet filtering can easily block more content than it is designed to," the group wrote in a separate blog post during the summer. "For example, if people do not understand what is being blocked and why, or if sites are incorrectly categorized."

And furthermore, if a site gets unfairly blocked and loses money because of it, it's unclear how it will be able to seek recourse.

"BT is not responsible for any of the site categorizations as these are done by our third party specialist vendor," BT responded to a series of questions posed by the group. "Our processes will ensure blocking errors are dealt with in a timely manner and each case will be dealt with on an individual basis."