A 24-hour Telstra network outage has wreaked havoc across the country, leaving businesses unable to use EFTPOS services and law enforcement incapable of tracking those on parole or under home detention.

Across the country on Friday morning, Australians were left confused as they were told EFTPOS devices and ATMs were down.

“We're currently experiencing an issue with some enterprise customer machine to machine (M2M) data services, which is impacting services including EFTPOS devices and ATMs. We apologise for the inconvenience and hope to resolve the issue as soon as possible,” Telstra tweeted.

As the telco worked on resolving the issue on Friday and Saturday, it urged customers to carry cash.

Taxis were left running on a cash only basis during the outage.

The outage was caused by “faulty vendor equipment” according to The Guardian.

At 12:35pm on Saturday, Telstra alerted users that the issue had been resolved.

But the damage had already been done for many.

Across social media, business owners complained of lost business – one Twitter user reporting “$8k customers walked away” during the outage.

The Telecommunications Industry Ombudsman later released a statement advising small businesses they may be entitled to business loss compensation.

Problems for law enforcement

Meanwhile in South Australia there were bigger problems for the Department for Correctional Services in South Australia.

CEO of the Department David Brown confirmed on Sunday that authorities were unable to track the electronic bracelets used to monitor 774 offenders across the state due to the outage.

One man who had been granted home detention bail on Thursday was left unaccounted for up until Monday morning.

State Premier Steven Marshall labelled the situation “unacceptable”.

"This is a very serious breach, a very serious outage and there will be a full and thorough investigation," he said.

"Clearly this is an unacceptable situation and clearly this is a situation that we cannot afford to occur in South Australia again.”

In May, a similar Telstra outage left 400 offenders across Queensland and the Northern Territory unaccounted for – some for up to four days.

The outage also impacted a number of Telstra’s online features, including MyAccount, Online Billing and the Telstra 24/7 app.