The city of Johannesburg, South Africa, has shut down its website and e-services after a group called the Shadow Kill Hackers broke into its network and demanded four Bitcoin in ransom.

On Thursday night, the city posted on Twitter to inform residents of "a network breach which resulted in an unauthorised access to our information systems." The incident is under investigation by Johannesburg's cybersecurity experts, who are working to mitigate the damage and have taken several customer-facing systems, including digital services and e-billing, offline.

Another tweet, from a separate account, contains the ransom note itself: "All of your servers and data have been hacked. We have dozens of backdoors inside your city. We have control of everything in your city. We can shut off everything with a button. We also compromised all passwords and sensitive data, such as finance and personal population information."

If attack group doesn't have the ransom by Oct. 28, it says it will upload the stolen data to the Internet. Four Bitcoin amounts to about 437,500 South African Rand, or $30,000 USD.

Around the same time as the attack, multiple banks also reported connectivity problems believed to be linked to cybercrime. Standard Bank and Absa are among those affected, reports local publiction BusinessDay. At least five banks are believed to be affected by the activity.

This is the second time Johannesburg has been hit with ransomware this year. In July attackers targeted City Power, a municipal entity delivering power to the entire city. The incident blocked residents from buying electricity, uploading invoices, and accessing City Power's website.

Read more details here.

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