“One of our subcontractors was hit by a digital attack, and that’s why our checkouts aren’t working any more,” Coop Sweden, which accounts for around 20 percent of the sector, said in a statement.
“We regret the situation and will do all we can to reopen swiftly,” the cooperative added.
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Coop Sweden did not name the subcontractor or reveal the hacking method used against it beginning on Friday evening.
But the Swedish subsidiary of the Visma software group said the problem was linked to a mayor cyber attack on US IT company Kaseya on Friday.
Kaseya has urged customers to shut down servers running its VSA platform after dozens were hit with ransomware attacks.
A wave of ransomware attacks has struck worldwide recently, especially in the United States.
Ransomware attacks typically involve locking away data in systems using encryption, making companies pay to regain access.
Last year, hackers extorted at least $18 billion using such software, according to security firm Emsisoft.
In recent weeks, such attacks have hit oil pipelines, health services and major firms, and made it onto the agenda of US President Joe Biden’s June meeting with Russian counterpart Vladimir Putin.