You know and I both know that Russians write crazy. Wacky stuff like хорошо and я забыл and очень приятно, which we couldn't type if our little English-language lives depended on it. Their alphabet is called Cyrillic, and is pretty awesome, but it isn't exactly what we're going to talk about today.
Imagine you're a Russian, trapped in a stupid computer system that won't let you type in Cyrillic. What the hell do you do? Sure, you can stoop to typing the pronunciations (horosho and ya zabil' and ochen' priyatno), but trying to spell things to other languages is never an exact science, and maybe you don't even know what Latin letters mean.
So you do the next best and most awesome thing: transletteration.
Transliteration is the process of going from one writing system to another letter-by-letter, usually keeping in line with the sound of the source text. So, я becomes 'ya' and ч becomes 'ch' etc etc. Transliteration is boring.
Transletteration is the process of going from one system to another, but trying to imitate the shapes, not sounds. A Cyrillic ч becomes 4, a б becomes 6, a я becomes R, and so on. That way the reader doesn't have to guess about the original spelling. Transletteration is awesome. EXAMPLES? YOU BET.
ХОРОШО: XOPOWO (horosho)
Я ЗАБЫЛ: R 3A6bl/\ (ya zabil')
ОЧЕНЬ ПРИАТНО: O4EHb nPNRTHO (ochen' priyatno)
It's like some terrifying version of leetspeak that isn't even in English! 50 4W350M3.
For Russian this is called Volapuk encoding, and originated from the Ye Olden Days of the Internet when nothing supported Cyrillic characters. Other alphabet sets have their own transletterations (Arabic [and another], Persian, Greek) with their own crazy rules.
I can't wait to get stranded somewhere with a Hindi keyboard and have to tap out some mishmash of Devanagari characters to fake an English alphabet.
Addendum!: Check out Gyaru-moji for the Japanese "young people" version of leetspeak, except without all of the hip cyber hacker parts.