In high nutrient evironments (ya know, when people feed a lot...) they breed like rabbits and annoying little tubes pop up everywhere and spread gross looking string across anything near them. I'm not a vermetid fan. The creepy little things can get freakishly big too. I've popped them with feeding tongs and done the superglue thing. Both work well depending on the circumstance.

If the rock is in quarantine, can't you try to eradicate them there and see if they reappear after a few days?