Hackers are targeting Apple customers with ransomware in the first successful attack against Mac computers, researchers with Palo Alto Networks Inc. told Reuters on Sunday. With ransomware, hackers demand users pay a stiff fee in hard-to-trace digital currencies to get an electronic key so they can regain access to their stolen data. Hackers used malware known as KeRanger, the first functioning ransomware to breach Apple’s Mac computers, through an infected copy of the BitTorrent app Transmission, according to Palo Alto Networks. When users downloaded the 2.90 version of Transmission, their Macs were infected. Transmission removed the malicious version of its software from the site and released a version Sunday that automatically removes the ransomware from infected computers.