I happened to visit this forum

http://www.woltlab.de/en/forum/main.php
Which is run by Woltab Burning Board (WBB)

It's an exact replica of vbulletin but it is free.
I am sure, they wouldn't have worked from scratch to make these pages resemble vBulletin. They could have just copied the vBulletin Files and sprinkled in some changes.
If this is the case, would it be a new form of piracy ?