The most terrifying one I've ever heard of was a major global bank[1] who received a call from a national telco about a bill for a leased line to one of their d

The most terrifying one I've ever heard of was a major global bank[1] who received a call from a national telco about a bill for a leased line to one of their data centers that had been unpaid for 6 months. They had no records of this line. The attacker had managed to get an unmonitored physical connection installed directly in their data center and was able to exfiltrate data completely without any limitation other than bandwidth for 6 months without detection. This story was never reported as far as I know. [1] I'm not going to name them but if the name came out I don't think anyone would be surprised who it was.