Sigh, it was all going so well. Had a short clash with zombie yak in my fortress that ended with creation of zombie catacombs for yak body deep in my fortress and yak skin and hair getting thrown outside to refuse pile. After that I sealed the fortress from outside world through a system of bridges, with atom smasher on the ready to smash any zombies that might try to get in.
2-3 migrants arrive and promptly die to lurking undead yak skin and hair. However, they wander away after a while and lurk near the edge of map, when new batch of migrants arrive, some 15 or so. I figure that well, I just might open the gates and let those migrants try their luck, hoping that 2-3 of them might make it through. As soon as I lower the bridge, nearly all my dwarves charge out to pick up the gear lying around from the 3 dwarves that met their unfortunate ending earlier, promptly getting their faces melted. I forbid everything, order survivors to burrows to salvage what I can, and few dwarves that are still alive scramble towards the fortress, followed closely by their zombie friends. I order lever pulled on defence atomsmasher, but due to construction error it is too close to the bridges, workers get scared by zombies and retreat. I order my military to go forth and slay those 2-3 zombies that are near the bridge and indeed, they dispatch the zombies easily with the help of elven caravan which just arrived. This gives clear sign to complete the command I gave earlier, a dwarf pulls the lever and my whole military along with the caravan is atomsmashed to oblivion. An assorted horde of 30-40 zombie dwarves, emus, wolves and kobolds, led by named yak skin, descend on my fortress, where last few survivors along with a random ghost barricade themselves in dining room, where they have ample food for emergency and a well for water.
I figure that I'll just tunnel out and dig to the caverns, when a forgotten beast arrives and starts lurking below. While I'm trying to come up with a new plan, a dwarf gets scared by a ghost, jumps down the well, drowns and raises as a zombie. He refuses to move, and since he is just 1z-level below, nobody can access water nor food. When next dwarf dies to dehydration, insanity overtakes the last 2 survivors, who start smacking each other.
At this point I just opened the doors and let the 50-something zombies in. It was a joy to watch.