[dustinfarris]

Letters like this go back and forth between companies all the time. It doesn't even sound threatening to me. Just a standard legal complaint. I'm sure there were a handful of phone calls made first. Sony and Twitter couldn't figure it out over the phone, so Sony sends the official letter saying, "here's why we're upset, this is what we want you to do about it, if you don't we will climb the legal ladder some more until it's all straightened out."