Back in 2003 or 2004, when I was trying online gaming for the first time (Ragnarok Online, Gunbound, DotA, etc), almost all gamer using “gua” (slang) opposed to “saya” or “aku” (standard) which means “I” or “me”. Later on, “gua” is switched to “gw” beacuse it's easier and faster to type.
Another word that changed was the laugh. Typing “hahaha” is too formal in gaming community because it's too ordinary as a laughing sound. We expressed laughing in many ways such as “bwahaha”, “huehuehue”, and also “huahuahua” to mock more the opponent.
The “huahuahua” word was simplified to be “hwhwhw” (remember of the word change from “gua” to “gw”). And instead of moving your right hand from your fancy gaming mouse into letter “h”, letter “k” is closer. Hence, the “wkwkwk” word was born.
It's widely used by online gamers. Later on when online based communication becoming more and more advanced in Indonesia, people who has gaming background had affect others in using “wkwkwk” as laughing sound.
It's based on my experience and assumption. Don't take it too seriously though. Wkwkwk.