K-rad was made popular in the 1980s by computer hacker circles. The word 'rad' reffered to a radical act performed by a hacker which deserved congratulations.
The term k-rad originated around the same time people started talking in numbers l1k3 th15. This type of language first started apearing on BBSes and FTP warez sites.
(I have the most leet, k-rad skillz on the net!)
Derived from Kilo (1000) * rad (see radical - meaning cool or amazing)
In keeping with computer terminology, its use was popular on dialup bulletin board systems (BBSes) in the 80s and early 90s, frequented by first and second generation hackers and computer enthusiasts.