I'm still using 6.03 because I dislike a few things with 6.12 and I have ignored all DCC's to avoid being exploited. Before I saw how to protect myself against the DCC exploit I was versioned by different users on a few networks and luckily my version reply wasn't mIRC so they did not crash my client, some of my friends did however get crashed because their reply was 6.1 and below.
