A Song of Ice and Fire series writer George RR Martin took time out from writing the sixth novel in his Game of Thrones-inspiring book series to appear on Conan O'Brien's US talk show.

During his appearance he talked about his writing process and most notably his tools of choice to avoid computer viruses. It's more interesting than it sounds.

"I have a secret weapon," said O'Brien. "I actually have two computers. A computer that I browse the internet with, get my email on and do my taxes on. Then I have my writing computer, which is a DOS machine not connected to the internet. I use WordStar 4.0 as my word processor."

WordStar 4.0 was released in 1987 on DOS [Disk Operating System) computers that were commonly used in the late 80s and early 90s.

Conan asked Martin why he'd stick with such an old machine.

"Well I actually like it, it does what I want a word processing programme to do and it doesn't do anything else. I don't want any help you know, I hate these modern systems where you type a lower case letter and it becomes a capital - I don't want a capital! If I wanted a capital I'd have typed a capital. I know how to work this."

Martin has been at work on sixth book The Winds of Winter since A Dance with Dragons was released in 2011. It was confirmed earlier this year that the book wouldn't be ready in time for 2014.

Martin has appeared on Conan before, dropping some pretty hilarious fake spoilers for HBO's Game of Thrones, such as how "Arya Stark discovers the ruins of the Statue of Liberty and realises she was on Earth the whole time".