The high court heard today that Mulcaire was involved in 'pinging' of mobile phones, a technique used to find the location of a users' handset through the cellular network.
The court was also told, as part of a civil case proceeding, that the investigator was guilty of computer hacking.
Only the police, security services and a few other select bodies are allowed to employ the practice of pinging. Using it for the purposes of the media constitutes a breach of privacy.
Mulcaire and News International have yet to respond to the claims, which form part of a series of civil cases over breach of privacy brought by hacking victims against News International, the former publisher of the News of the World, reports BBC News.
Five "lead cases" are due to start in January against News International, including actor Jude Law, sports agent Sky Andrew, footballer Paul Gascoigne, solicitor Graham Shear and Sheila Henry, whose son was killed in the London 7/7 bombings.
These cases have been selected to reflect the diverse victims involved, and they will be heard quickly in order to give other claimants an idea of the issues outlined and the level of damages recovered.
This will enable the more than 60 other people that have lodged hacking writs against News International to judge whether they wish to pursue their own actions against the firm.
During today's hearing, justice Vos insisted that the test cases were not about a "witch hunt", and he was not going to allow a "mini-Leveson Inquiry", referring to the judge-led inquiry into phone hacking which launched on Monday.
Speaking to lawyers for News International, justice Vos - who will hear the cases in the New Year - said: "It is not a witch hunt. It is not a crusade. It is to determine the damages you must fairly pay."
The High Court heard claims that a number of computer hard drives had been destroyed by News International after the publisher moved offices in late 2010.
The Metropolitan Police launched Operation Tuleta in July, investigating allegations of computer hacking against News International, running alongside the Operation Weeting phone hacking probe. Operation Tuleta is investigating apparent breaches of privacy reported to the police since January.
Last month, Labour MP and culture committee member Tom Watson warned shareholders in Rupert Murdoch's News Corporation of "Mulcaire 2" in the UK, saying that victims of alleged computer hacking were ready to take action against the News Corp-owned News International.
"You haven't told any of your investors what is to come," he told Murdoch at News Corp's annual meeting, adding that the Met police was investigating computer hacking by private investigators who had worked for the News of the World and other newspapers.
It has also been revealed in the high court that the mother of actor Hugh Grant's baby daughter had been granted an injunction because of her "unbearable" treatment by the paparazzi.