"Transmission" by Hari Kunzru, Page 101: "Finally, after an interminable crunch and a stutter from inside the case, a message appeared in front of him.

u r a pr1z0n7r ov th3 l0rd$ ov m1zr00L"

In the geek/nerd/gaming world, some people tend to use numbers and symbols to represent letters. For example, an 'i' becomes a '1', or an 'S' becomes an '$'. This is commonly referred to as either elite chat, or most commonly abbreviated to 'leet speak' (1337 speak). This kind of chat is mostly common in Junior High and possibly Middle Schoolers, but there are extreme geeks who are much older that still use this. the extreme geeks use it in a way of talking down to someone. For example, if you do something they feel is poor or retarded, they'll call you a 'n00b' or 'n00bilicious'. Today people normally use it to poke fun at those that use it in seriousness.

In reference to the text, this concept solidifies Arjun's geeky status even more, and can remind us of some of his co-workers (Darryl perhaps?).

As far as what the statement means, the virus coders are basically making sure the infected computer's owner knows he's been infected and who did it. We can safely assume that the lords of mizrool are what the group of coders call themselves - a trademark if you will. I tried searching for lords of mizrool and returned nothing.

Wikipedia: Leet Speak