It was a Friday in June, a short workday before a public holiday weekend in Ukraine, and cybersecurity expert Victor Zhora had left the capital, Kyiv, and was in the western city of Lviv when he got the first in a torrent of phone calls from frantic clients.
His clients’ networks were being crippled by ransomware known as Petya, a malicious software that locks up infected computers and data. But this ransomware was a variant of an older one and wasn’t designed to extort money — the goal of the virus’ designers was massive disruption to Ukraine’s economy.