Long before Facebook bought Oculus VR for $2 billion — before Oculus even launched its successful Kickstarter campaign — famed video game programmer John Carmack sparked a wave of interest in the virtual reality headset by showing off an early duct-taped prototype at game conventions. Now, it may come back to bite Oculus and Facebook in the ass. Now that John Carmack works for Oculus, his former employer ZeniMax Media claims that it owns part of the intellectual property in the headset, and may sue Facebook and Oculus over those ideas in the near future.

The Wall Street Journal obtained two letters from ZeniMax lawyers sent to Oculus and Facebook, which claim that Carmack's contributions were invaluable to the initial success of the Rift: "It was only through the concerted efforts of Mr. Carmack, using technology developed over many years at, and owned by, ZeniMax, that [Oculus founder Palmer] Luckey was able to transform his garage-based pipe dream into a working reality," the letter reportedly reads.

"ZeniMax provided necessary VR technology and other valuable assistance to Palmer Luckey and other Oculus employees"

"ZeniMax provided necessary VR technology and other valuable assistance to Palmer Luckey and other Oculus employees in 2012 and 2013 to make the Oculus Rift a viable VR product, superior to other VR market offerings," said ZeniMax in a statement to The Verge. "The proprietary technology and know-how Mr. Carmack developed when he was a ZeniMax employee, and used by Oculus, are owned by ZeniMax."

ZeniMax claims, and The Verge has confirmed, that Luckey signed a non-disclosure and non-ownership agreement in 2012 that covered some form of VR technology, though it's not clear what it included. The company also says that Oculus was aware of the issue well before the Facebook buyout. ZeniMax and Oculus "previously attempted to reach an agreement whereby ZeniMax would be compensated for its intellectual property through equity ownership in Oculus but were unable to reach a satisfactory resolution," says a spokesperson.

In a statement to The Verge, Oculus ridiculed the idea. "It's unfortunate, but when there's this type of transaction, people come out of the woodwork with ridiculous and absurd claims. We intend to vigorously defend Oculus and its investors to the fullest extent," wrote a company representive.

The original Oculus Rift prototype, as shown off by John Carmack

However, Oculus could be more vulnerable than you'd think to such threats. The Oculus Rift is unusual in the consumer technology space in that Oculus owns very little intellectual property on the physical hardware, in part because its key ingredients were openly developed at a research lab where Oculus founder Palmer Luckey was an intern. That's not to say that ZeniMax necessarily owns Carmack's work on virtual reality, which he openly discussed on the web, but Oculus may not be able to defend itself simply by pulling out a stack of patents.

And, at least according to the Journal's anonymous sources, ZeniMax isn't a Johnny-come-lately that's only asking for money now that Facebook dropped $2 billion for the virtual reality company. The Journal reports that Zenimax became interested back in August 2012, back when the Oculus Rift Kickstarter campaign began. That seems odd, though, particularly given comments made at the time Carmack and ZeniMax parted ways. Carmack said he actually left the studio he founded, id Sofware, because owner ZeniMax didn't want him working on virtual reality.

Even if the claim turns out to be bunk, it could be interesting and costly if Oculus and new owner Facebook are forced to prove it in court. John Carmack says that his work at ZeniMax wasn't patented either, so ZeniMax may need to prove that Oculus is using its proprietary code and ideas in order to force a settlement or reach a favorable verdict.

Update May 1st, 2014 3:15pm: Updated with comment from ZeniMax and John Carmack's tweet.