Several victims of black-taxi rapist John Worboys learned of the decision to release him from prison in the media, an official review has revealed.
Women who found out through press reports included those who were signed up to a scheme designed to keep them up to date on the case.
Correspondence to victims contained errors, while letters disclosing Worboys was to be freed did not convey the consequences in a "readily understandable" way.
The findings came as Worboys appeared at a High Court hearing in which two victims are seeking permission to mount a legal challenge over the decision to release him.
Chief Inspector of Probation Dame Glenys Stacey was asked by the Government to carry out an urgent review of contact with Worboys's victims after authorities came under fierce criticism over their handling of the case.
Her report said that by and large the National Probation Service appeared to have complied with instructions that were relevant at the time.
After Worboys was sentenced in 2009, 12 victims who fell under the statutory Victim Contact Scheme (VSC) were contacted and given the opportunity to opt in. Four chose to do so, and over time contact was lost with one.
The quality of correspondence sent over the period of Worboys's sentence was described as poor.
"Some letters contained errors in victims' names and addresses, and the messages were not conveyed clearly," Dame Glenys's report said.
Prior to Worboys' parole hearing in November, the NPS attempted to contact women who were not signed up to the scheme which was a "well-intentioned action".
But there was not enough time before the hearing for women to receive and absorb the information, while the letters "lacked clarity and urgency".
By the time of the parole hearing, five women were in contact with the VCS and the probation service took prompt action to notify each of the decision to release Worboys.
Notifications were given by letter, email or phone call, depending on choices made by women previously.
The review said: "Inevitably, they each received the news at different times, and regrettably the news broke in the press before some had received and read the notification.
"Those women not in contact with the scheme - the majority - learnt of the decision through the media. All who spoke to us described their shock and distress. They had not felt prepared for this outcome."
Most of the women spoken to by the review found out Worboys was set to be freed in the media on or around January 4.
"Their distress, anxiety and disbelief at finding out that John Worboys was to be released from custody was palpable," the report said.
One woman found out about the news in the media after an email was automatically forwarded to her "junk" folder.
Correspondence about Worboys's release used a templated format and the style and language was "not wholly appropriate".
"For example, the term 'disappointing' - as applied to the reaction the women may have to the news of John Worboys' release - did not, in our view, demonstrate sufficient gravitas or empathy," the report said.
Justice Secretary David Gauke said: "It is reassuring that the correct procedures were followed and that in some respects victim liaison officers have gone above and beyond the victim contact requirements.
"However, I fully accept that there are things we can do much better.
"That's why we have already changed the letters we send to victims to make them more compassionate, clearer and more informative, but there is more to do. We will take these findings and improve the system."
Worboys, 60, was jailed indefinitely, with a minimum term of eight years, for drugging and sexually assaulting women passengers.
He was convicted of 19 offences relating to 12 women but has been linked to more than 100 complaints in total.