Online security has been tightened at ACC after some claimants bugged emails to see what case managers were doing.
Bronwyn Pullar, the woman at the centre of the ACC security scandal, has revealed she used email tracking software to get updates of activity with her file - a detail already revealed by Michelle Boag to ACC minister Judith Collins.
It is the latest twist in a scandal which has engulfed the National Party, pitted former president Boag against her political friends, cost former ACC minister Nick Smith his Cabinet job and embroiled Prime Minister John Key.
An investigation by the Privacy Commissioner is under way into the accidental sending of client information to Pullar. Police are also investigating ACC's claim Pullar tried to trade the information for a benefit.
Pullar identified a staff member who had opened her email before it became public, exposing the bug she had planted in her email, feeding information back to her.
The Herald on Sunday understands a review by ACC identified other claimants were using similar tactics to monitor their claims.
A spokeswoman said: "ACC tightened its IT security following revelations that email tracking software was being used to track emails sent to the organisation without the knowledge of the recipients."
The existence of the bug in the email had already been revealed by Boag to Collins. In the email leaked to the Herald on Sunday which exposed Pullar's identity, Boag wrote: "You should also be aware that Bronwyn has an email tracking device that allows her to know when her emails are opened."
Meanwhile, a man who received claimants' confidential information intended for ACC for three years says the corporation stopped the stream of information only after he billed them for fax machine toner and paper.
Jon Styles, of Style Group, an acoustic consulting company based in Parnell, said he started getting faxes from different ACC suppliers to his office about three years ago.
"The faxes were mainly from treatment providers and comprised claims for expenses and cited the names and contact details of the individuals concerned and also details of their treatment," he said.
He said he did not know why he was receiving the faxes and tried sending them back and alerting ACC.
"Sometimes the faxes could involve up to 40 pages of supporting documents for the claims which would clog up our fax line for ages and use up our toner and paper. Eventually I got so fed up, I decided to invoice ACC for the lost time, paper and toner - an amount of something like $350 plus GST. Only this action got ACC to listen," he said.
"After much debate and issuing a credit for the invoice, I stopped receiving faxes." He shredded all the faxes he received.
ACC spokeswoman Stephanie Melville said ACC was sorry it took so long to stop the faxes.
ACC beneficiaries Mike Rogerson and Garth Paul have also reported being sent other claimants' files.