But the former special forces soldier, 42, denied his motive was to avoid detection by military or police investigators.
“I simply did not trust they (the media and their sources) were not trying to intercept my communications,” he told the Federal Court on Wednesday.
“The News of the World thing was playing heavily on my mind.”
Roberts-Smith continued giving evidence in his case against media companies over a series of articles published in June 2018 he says defamed him by portraying him as a war criminal.
The publishers have pleaded a truth defence.
“I couldn’t believe what was going on,” he said, recalling his thoughts when reading the first article on The Age’s website on June 9.
“It was demonstrably false and my recollection initially was quite vague because we hadn’t talked about it in a while.”
He set about calling former colleagues from his personal phone to theirs, to patch together where people had been in each mission, the missions’ routes and who assaulted what areas because most of what had been written “was wrong and false”.
Then he said he became concerned someone else could be listening in.
The people he suspected were talking to the media had the technical skills to intercept communications, he said.
That led the country’s most decorated soldier to ask a mutual friend, through his then-wife Emma Roberts, to get some prepaid mobiles.
“It was reasonably evident Person 6 and Person 7 were the key drivers of the campaign,” he said, referring to two anonymised soldiers.
The first set of articles – titled SAS’s Day of Shame and Troops Kept ‘Kill Board’ – detailed the allegation that a special forces soldier had kicked handcuffed shepherd Ali Jan off a cliff in Afghanistan.
While Mr Roberts-Smith wasn’t named in the first set of articles, he said he was in no doubt it was about him.
Family and friends also cottoned on, and he spent the weekend fielding calls from them and high-profile figures including then-Australian War Memorial director Brendan Nelson and former federal police commissioner Mick Keelty.
He said he didn’t learn he was being investigated by any civilian or military investigators until an August 2018 article about police looking into an allegation he committed a domestic violence assault in a Canberra hotel room.
Roberts-Smith is also suing over that article, arguing they were false and made him out to be a “deplorable human being”.
“At that point, given the timing and the articles previously, I had so much anxiety and was so unable to engage with people publicly and, now having been named, I actually started thinking my life was over,” he said.
The publishers of the Sydney Morning Herald, The Age and The Canberra Times says the claims made in the August 2018 article were substantially true.