I think mine's on zork (?) I am completely daft about how it works, I just set it up for people who would like to talk... complete coward as far as Mods or anything like that goes.
I just found a topic in the phpBB.com support forum:
Apparently it's happening quite a lot, and strangely in the last couple of weeks.
My board only has one or two people online at a time, so if there's a problem with 'open connections' from traffic as they say in the phpBB topic, it would have to be because it's being tampered with somehow.
Maybe you can make some sense out of what they're saying? It's pretty discouraging to find that blank page. :\