The government has apologised after Emily Maitlis received a letter from a man, who harassed her for two decades, while he was in prison.
A former friend of the Newsnight presenter, Edward Vines, was jailed on Tuesday for a further 45 months for breaching a restraining order.
He wrote to the BBC journalist while in HMP Bullingdon and again while living in a bail hostel.
The Ministry of Justice apologised for "the distress caused to the victim".
Judge Peter Ross said the situation was "wholly unsatisfactory" and has given the Probation Service and the Bicester prison's governor 10 days to provide an explanation.
An MoJ spokesperson said: "We apologise unreservedly for this error and for the distress caused to the victim.
"We have significantly strengthened our monitoring procedures to prevent incidents like this from happening again.
"We would like to reassure the victim that any future correspondence involving this offender will be carefully checked, with staff reminded of the sensitivities of this particular case."
In a statement read to Oxford Crown Court, Ms Maitlis said she had felt "scared and let down" after she heard Vines had breached the restraining order "even from within the prison system".
She said it had affected her relationship with her husband, and scared her children, "who thought the threats had gone away... while he was behind bars".
Vines, 47, was first convicted of harassing Ms Maitlis in 2002 and had subjected her to "psychological torture" by continuing to contact her, Judge Ross said.
The presenter first met Vines, of Clarkes Row, Oxford, when they were students at Cambridge University.
He was issued with an indefinite restraining order in 2009, which he was convicted of twice breaching last year.