US software firm Kaseya is set to restart after a huge ransomware attack

A US software firm hit by a major ransomware attack that crippled hundreds of companies worldwide said it was on track to restart its servers later Tuesday to bring customers back online.

Kaseya, the Miami-based IT company at the centre of the hack, said it pushed back its forecast by two hours and hoped to resume operations between 2000 and 2300 GMT.

The news comes after an unprecedented attack that affected an estimated 1,500 businesses and prompted a ransom demand of $70 million.

The systems were being brought back online with "enhanced security measures" and "the ability to quarantine and isolate files and entire ... servers" in case of infection.

"Later today we will release a customer-ready statement for you to use to communicate to your customers on the incident and the security measures that we have put in place," a Kaseya statement said.

While Kaseya is little known to the public, analysts say it was a ripe target as its software is used by thousands of companies, allowing the hackers to paralyze a huge number of businesses with a single blow.

Kaseya provides IT services to some 40,000 businesses globally, some of whom in turn manage the computer systems of other businesses.