Sentence:  The use of algorithms in policing is one example of their increasing influence on our lives....who, if anyone, is policing their use[?] Such concerns were sharpened further by the continuing revelations about how the US National Security Agency (NSA) has been using algorithms to help it interpret the colossal amounts of data it has collected from its <WSD>covert</WSD> dragnet of international telecommunications. 
Meaning of the word marked with <WSD> tags:  Secret, surreptitious, concealed.