When it comes to the web, the words safe and secure do not exist, experts said in reaction to the recent ransomware attack on Joburg City Power.

Several of City Power’s IT applications and networks were affected by a cyberattack on Thursday that prevented customers from buying prepaid electricity or accessing the website to log faults and invoices. By Friday morning, the server, which supplies large power users, including mines, factories, shopping malls and hospitals, was restored.

This latest attack caused blackouts across Joburg as cybercriminals took control of the city’s power servers, preventing residents from purchasing electricity...