US carriers Verizon and AT&T are snooping at the online activity of its more than 100 million mobile customers, the reports released by Electronic Frontier Foundation and multiple news outlets said.

According to the reports, both the service providers have inserted a special code, called ‘supercookie’, into the cellular web traffic of their networks.

Sources said that this code is being used by the telecom giants to track the online activity of their customers, including their browsing habits, duration spent, content browsed and others. The sources added further that Verizon will also be using the data to help marketing firms send mobile users the targeted advertisements.

A report by The Washington Post has mentioned similar snooping behavior of Verizon, saying the telecommunication firm has been keeping a track record of its 106 million retail customers — including those without government or business contracts — since 2012.

AT&T, on the other hand, is examining a similar monitoring system for ad purposes.

The customers who wish to know their status on being tracked by the companies can do so by using tools like ‘AmIBeingTracked.com’.

The snooping of customers’ online activity by their service providers is not new. Earlier tech giants like search engine Google and social networking site Facebook have long used tools such as cookies or numerical identifiers travelling with users between sites, to keep a track on their customers’ browsing habits and send relevant advertisement.

But Verizon and AT&T’s snooping activity seems to be very unprecedented. Unlike normal cookies, their supercookies cannot be deleted with the clearing browser data tool. As the markers are included at the network level, hence, the customers are tracked at all levels regardless of which sites they visit.