A hidden application found on millions of smartphones can log almost everything a user does, claims a US security researcher. Trevor Eckhart unearthed the Carrier IQ application that runs largely unseen on Android, Nokia and Blackberry handsets. Mr Eckhart said the software could log locations, websites visited, key presses and many other parameters. Carrier IQ denied its code was spying. It threatened Mr Eckhart with legal action but later backed down. Mr Eckhart said he found Carrier IQ via work he had done on a security programme, called Logging Test, which spotted which apps were running on an Android phone. His analysis revealed that Carrier IQ could be set up to record almost anything and everything done on a smartphone. The code has been found on Nokia, Blackberry and Android smartphones and tablets. A cut down version has also been seen running on some Apple phones. In response, Carrier IQ defended its software, saying it was not spying on users. It said the code was used by mobile operators as a diagnostic tool to spot what was causing calls to drop, texts to go astray and battery power to be drained. Mr Eckhart claimed Carrier IQ was buried deep in the core code for a smartphone to prevent it being found and, on some phones, was customised to prevent users changing what it logged. In some cases, he said, only those with advanced skills would be able to find it. He put a video on YouTube which showed Carrier IQ logging button presses, search queries and locations. Much of the data had been grabbed without consent, he said. BBC