Been using the security token since before FFXIV (wanted that mog satchel), on a static IP, and I only have 1 machine I can log into FFXIV with, and I haven't gotten that message yet.

I've even crashed and logged back in too soon and the most I get is a login error because my character hasn't been logged off yet, but never anything talking about suspicious activity or the need to reset my password.

So I'm inclined to believe it's that dynamic IP deal over crashing or anything like that. Whether or not the token solves the problem... Well, I've never not had the token for FFXIV, so I can't verify that.