On Sunday researchers discovered what is believed to be the world’s first ransomware that specifically targets OS X machines.

The KeRanger malware, which imposes a 72-hour lockout window unless the victim pays 1 bitcoin (approximately $410), appears to have been first discovered via a rogue version of Transmission, a popular BitTorrent client.

James Maude, Senior Security Engineer at Avecto commented:

"Ransomware has rapidly become one of the biggest cyber threats around. From early strains of CryptoLocker to the latest Locky variants it has become big business for cyber criminals. As with any successful business they are constantly looking to expand by targeting websites, mobile devices and now Apple Macs.

"This represents an interesting twist in the tale of Mac malware as previously many strains first appeared hidden in pirated software on torrent sites. In this case the attackers seems to have targeted the torrent client itself rather than the downloads. As with most Mac malware this strain is exploiting the fact that users routinely login with privileged admin accounts and are free to download and install software from unknown sources. In this case the Gatekeeper check was bypassed using a genuine developer certificate, but as researcher Patrick Wardle has previously demonstrated there are plenty of ways an attacker can bypass Apple’s built-in security boundaries.

"In the enterprise this problem is often magnified by the fact OS X users are logging on to devices with full admin accounts. KeRanger exploits the fact that the user has an admin account to install itself into the system library folder and infect the OS. On the Windows platform provisioning all your users with admin account is unthinkable, but when it comes to Macs organisations often 'think different'.

"Macs in the enterprise are increasingly becoming the weak link in security that attackers are all too happy to exploit. We are seeing an increasing number of malware strains and attacks targeting Mac users who are often left almost unprotected. Our advice is to follow the same best practice on all your devices no matter what the operating system is: patching, least privilege and whitelisting applications."