WASHINGTON: Between 800 and 1,500 businesses around the world have been affected by a ransomware attack centered on US information technology firm Kaseya, its chief executive said on Monday.

Fred Voccola, the Florida-based company's CEO, said in an interview that it was hard to estimate the precise impact of Friday's attack because those hit were mainly customers of Kaseya's customers.

Kaseya is a software company which provides software tools to IT outsourcing shops: companies that typically handle back-office work for companies too small or modestly resourced to have their own tech departments.

One of those tools was subverted on Friday, allowing the hackers to paralyze hundreds of businesses on all five continents.

Although most of those affected have been small businesses - like dentists' offices or accountants - the disruption has been felt more keenly in Sweden, where hundreds of supermarkets had to close because their cash registers were inoperative, or New Zealand, where schools and kindergartens were knocked offline.

The hackers who claimed responsibility for the breach have demanded $70 million to restore all the affected businesses' data, although they have indicated a willingness to temper their demands in private conversations with a cybersecurity expert and with Reuters.

"We are always ready to negotiate," a representative of the hackers told Reuters earlier Monday. The representative, who spoke via a chat interface on the hackers' website, didn't provide their name.

Voccola refused to say whether he was ready to take the hackers up on the offer.

"I can't comment 'yes,' 'no,' or 'maybe'," he said when asked whether his company would talk to or pay the hackers. "No comment on anything to do with negotiating with terrorists in any way."

On Sunday, the White House said it was reaching out to victims of the outbreak "to provide assistance based upon an assessment of national risk."