Electronic ankle bracelets used to track criminals in the NT and Queensland stopped working when Telstra's network was hit by outages.
Northern Territory authorities lost contact with 85 criminals wearing electronic ankle tags for up to four days after a key part of Telstra's network dropped out.
The outage that affected the network's mobile G4S service on May 4 meant that Correctional Services officials had problems keeping track of where the offenders were in the community.
"At 8.10am May 4 there were approximately 85 electronic monitoring devices identified as having unresolved communication issues," an NT Corrections spokesman told the NT News on Tuesday.
"By 11.30am, 23 had been resolved. By Saturday, May 5, seven remained unresolved."
The spokesman said the monitoring devices were all finally restored by May 8.
The department's website says the electronic tags are used to monitor offenders whose movements are restricted, including those on home detention, or who are not allowed to go to certain places such as a park or school.
The devices use Global Positioning Satellite (GPS) technology to help authorities monitor the location of offenders.
At the time, Telstra said outages to its services had been caused by damage to a fibre link after a cable pit in NSW's central west was hit by lightning.
The damage caused some triple-zero calls to drop out for 10 hours across five states.
AAP is seeking comment from the NT's Department of Correctional Services.
Telstra told SBS News: "Telstra provides sim cards to G4S Australia for remote monitoring devices. In an instance of network disruption, the devices should automatically reconnect when the network is restored. In the case of all outages, Telstra works to restore services as quickly as possible."
G4S Security, which leases the devices to state agencies, refused to provide comment to SBS News and referred queries to NT Corrective Services.
Queensland monitoring devices hit
Queensland Corrective Services told ABC that monitoring devices in the state were hit by a Telstra outage on May 4.
QCS immediately put contingency processes into place to ensure public safety, and escalated the incident to the service provider for priority resolution," a QCS spokeswoman told the ABC.
"Offenders have no way of knowing when the devices are not operational. Nearly 300 individuals are monitored using similar GPS devices in Queensland, including high-risk offenders and those on parole. 299 devices were affected by the outage, QCS has confirmed."
The spokeswoman said the agency used other contingency plans, while the ABC reports no serious breaches occured during the 45-minute outage.
Telstra blames software fault
Telstra has blamed a software fault for its second widespread network outage in a month, which left customers unable to make calls or use mobile data.
The telecommunications giant said a software fault triggered multiple elements across its 4G network to fail, and a further fault caused an interruption on its backup hardware, which resulted in customers dropping back to the 3G network.
There was then a significant disruption to 3G voice and data services as the network became flooded with data traffic.
Telstra is yet to disclose how many customers were affected by Monday's outage but said it took about two hours to restore full service.
A map produced by fault tracking site Aussie Outages on Monday showed the problem affected a number of hubs around the country, including in Sydney, Hobart, Brisbane, Melbourne, Perth and Adelaide.
The company said it is still investigating the root cause of the software fault and is working closely with technology vendors on the specific element of software which triggered the issue.
"Our teams have worked around the clock to restore services and to investigate why the redundancy in our network did not prevent customer impact, for which we are deeply sorry," Telstra said on Tuesday.
"We will continue to closely monitor network stability and performance."
Telstra group managing director networks, Mike Wright, on Monday apologised to customers but denied the disruption had anything to do with outrage problems earlier in the month where customers were unable to make or receive calls following issues with the 4G network.
Earlier in May, Telstra customers were affected by issues with the company's 4G network caused by technical changes made ahead of upgrades to equipment in Melbourne.
A couple of days later, triple-0 voice calls were affected across three states after a Telstra cable running between the regional centre of Orange and Bowral in southern NSW was damaged by what appeared to have been a lightning strike.
The issue resulted in problems with calls to the police, ambulance and fire brigade numbers in NSW, Victoria, Western Australia, South Australia and Tasmania.
Telstra shares are at a seven-year low, and were trading 2.9 per cent lower at $2.72 by midday on Tuesday.