The Sun-Herald says security was increased at RA's headquarters at Moore Park, where staff were told not to prop lower level doors open. Castle's Sydney home was given a security review.
"She was subjected to vitriol on social media as well as public criticism for a number of different reasons on a scale that few Australian sporting administrators have had to endure," the Sun-Herald reported.
New Zealander Castle quit last week, after two-and-a-half years in charge, after it turned out she did not have her board's total support.
McLean said: "I'm not a social media person, but I'm aware of some of the things that were said over a period of time in a quite vicious and vitriolic way.
"It's the silent forces, the dark forces, they're the things that upset me most.
"It's the people who didn't know the facts or were just one of those faceless people out there - that was the damaging thing form her perspective.
"She shared some of that with me, which I found quite abhorrent.
"One of my greatest concerns with her was her welfare and how she was on a daily basis. A lesser person would have thrown the towel in ages ago, quite simply."
One of Raelene Castle's fiercest critics, former Wallabies coach turned broadcaster Alan Jones, was scathing of her performance but also said her exit as Rugby Australia CEO doesn't solve anything because the RA board is equally to blame for the sad state of rugby in Australia.
On his 2GB radio show on Friday morning, Jones ripped into Castle for a string of poor decisions but also called for a cleanout of RA chairman Paul McLean and the rest of the board, who signed off on the CEO's calls.
"This solves absolutely nothing. I have said all along it's easy to throw Raelene Castle under the bus," Jones said.
"I can't imagine anything she has done, whether it's the bloated expenditure, the ridiculous growth in staff of over 150, the foolish, personal and spiteful attack on Israel Folau, the hopeless performances off the paddock and on the paddock. All of these things have been endorsed by the board.
"Now the board have told Raelene Castle, 'You must go, we need clear air'. You won't get clear air with the departure of Raelene Castle. The whole kit and caboodle have to go, that's what the Wallaby captains (who sent RA a letter this week demanding a change in leadership) wrote about.
"And that's the only way sponsors will return, the public will return, it's the only way credibility can be regained.
"I've no doubt Raelene Castle did her best. It's an appointment that shouldn't have been made. She knows nothing about the game. It's like putting someone to become the first violinist in the Sydney Symphony Orchestra who can't read music.
"Paul McLean is the acting chairman. He's been present for every one of the decisions that Raelene Castle made, every one of them, and so have the bulk of the board."
Jones also denied the attacks on Castle had anything to do with her gender.
"It is insulting to say this is a matter of gender," Jones said. "It's got nothing to do with Raelene Castle being a woman. It is totally related to the results and the effectiveness of the performance."
New Zealand Rugby also weighed in on Castle's resignation, though was much more positive than Jones, releasing a statement that praised her "unselfish" decision.
"New Zealand Rugby (NZR) would like to acknowledge the commitment, hard work and dedication Rugby Australia chief executive, Raelene Castle, has given to rugby in Australia and as our colleague on Sanzaar and at World Rugby," the statement said.
Castle, in one of her last interviews before resigning, had talked positively about her working relationship with NZ Rugby.
"We've worked hard on those relationships," she told Newstalk ZB.
"When things get tough Anzacs come together and work together – that's the reality of the engagements we're having with New Zealand Rugby. We've both got to make decisions that are right for our own businesses, but we realise that we're stronger together."
NZR shared a similar sentiment.
"NZR has always enjoyed a special and close relationship with Rugby Australia and Raelene has worked hard to both enhance and strengthen that. We have enjoyed working with her and are sad to see her go, however we respect her decision to resign.
"It says a lot about Raelene's character that while we consider that she still has much to contribute to Rugby Australia, she has taken an unselfish look at what is best for the game in Australia.
"NZR wishes Raelene all the very best and thanks her for her contribution to rugby."
