The City of Johannesburg reported a breach of its network on Thursday night and shut down its website and all e-services, hours after receiving a bitcoin ransom note from a group called the Shadow Kill Hackers.

The hack occurred at the same time that several banks also reported internet problems believed to be related to cyber attacks.

In a message on Twitter  posted just after 11pm the city said it had “detected a network breach which resulted in an unauthorised access to our information systems”.

“The incident is currently being investigated by City of Joburg cyber security experts, who have taken immediate and appropriate action to reinforce security measures to mitigate any potential impacts. As a result several customer facing systems — including the city’s website, e-services and billing systems — have been shut down as a precaution.”

Customers will not be able to transact on e-services nor log queries via the call centre.

The note on Twitter came after several city employees received the ransom note, which reads: “All your servers and data have been hacked. We have dozens of back doors inside your city. We have control of everything in your city. We also compromised all passwords and sensitive data such as finance and personal population information.”

The hackers then demanded the payment of 4.0 bitcoins by October 28 at 5pm failing which they will upload all the data onto the internet.

Both Standard Bank and Absa informed customers on Thursday of the internet problem, but at least five banks are believed to be affected.