Dan Evans, 38, initially lied about trying to access the voicemail messages of designer Kelly Hoppen, the former stepmother of the actress Sienna Miller, in 2009.
He was quizzed at the Old Bailey over his first prepared statement to police, which attributed "sticky keys" on his phone for misdialling.
The prosecution witness told the hacking trial it had come from a draft statement drawn up for a News International supply company.
He told the court that the lawyers at the time were employed by News International and not him.
Describing how it came about, he said: "Not long after I had my first meeting, a document had been put together where sticky keys already had a fairly prominent position.
"It formed the basis of future drafts and ultimately it was the defence that went forward."
Asked by the judge Mr Justice Saunders what "sticky keys" actually meant, he said: "I'm not really sure. I said this is one of the things that's wrong with the phone, why I'm not using it any longer.
"I described it thus and it became this defence for News International."
Mr Saunders pointed out that Mr Evans had the opportunity to change the defence if he wanted to, to which the witness said: "Yes, absolutely."
Mr Evans also told the jury "there was a lot more" material about hacking relating to the Sunday Mirror that they had not been told about.
Former NotW editor Andy Coulson, 46, of Charing, Kent, denies conspiring to hack phones and commit misconduct in a public office.
All seven defendants in the case, including former editor Rebekah Brooks, have denied the charges against them.
The trial continues.