Until legally proven otherwise (which we cannot do without the actual source code TX has), its not a copyright violation. Its highly assumed to be a copyright violation based on the evidence certain hackers have shared but it has not been officially/definitively proven.M'kay...
From the GPL2 Preamble:
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.