Torrenters beware! The first ransomware attack on Mac users in the wild has been discovered, “courtesy” of Transmission, a BitTorrent client for Mac.

The torrent service received a major update last week, but it unfortunately the new software happened to be infected with ransomware, which went on to quietly install itself on the the Macs of everyone who downloaded the update from Transmission’s website.

Apple has touted the Mac’s resistance to viruses for decades as a selling point over Windows PCs, but a team of researchers have created a new firmware worm for Mac that might just make you want to go back to doing work on good old pencil and paper.

Two white-hat hackers discovered that several vulnerabilities affecting PC makers can also bypass Apple’s renowned security to wreak havoc on Mac firmware. The two created a proof-of-concept of the worm called Thunderstrike 2 that allows firmware attacks to be spread automatically from Mac to Mac. Devices don’t even need to be networked for the worm to spread, and once it’s infected your machine the only way to remove it is to open up your Mac and manually reflash the chip.

Here’s a preview of Thunderstrike 2 in action: