Martin has a backup running on his computer all the time, and he's worried that malware can get onto it. Leo says that current malware is "wormable" and can actually take advantage of Microsoft's networking, spreading through the network. It's called "eternal blue." So if you have hot storage that's online and current, you have to treat it as vulnerable. The only real good backup is a disconnectable backup.
Hackers somehow got ahold of a malware exploit that was developed by the NSA and used it to attack the city of Baltimore. The malware, a ransomeware exploit known as Eternal Blue, was taken home by an NSA contractor, and Leo says that Kaspersky antivirus quarantined the malware and then sent it to the home office in Russia.