It appears one of the guys over at The Defaced Security Team have got their hands on the files needed to host your own Battlefield 3 beta server. Initial reports suggest it is possible to have a server hosted on your PC listed on the master server list accessible by anyone. Two servers have currently been spotted; one such server showing as many as 128 player slots. Whilst many fans of Battlefield had been annoyed at the exclusion of Caspian Border, the leaked files unfortunately do not include the Caspian Border map and is therefore unlikely to excite the majority of Battlefield players.
DICE made this comment on the situation:
We are aware that a number of servers have appeared and are running game modes and player counts that have not currently been seen. Please try to remain on official servers.
Official servers run the following configuration
Max Players: 32
Map: Operation Metro
Please avoid temptation and remain on these official servers while we work to have these servers dealt with.
Playing on those servers can cause your account to become compromised, stats to be altered or other issues to arise which may lead to having your account banned by EA.