In 2005, Andrew Tridgell, the developer of the Samba file server and the open-source version control system Mercurial, was accused of violating the terms of service of the proprietary version control system BitKeeper. Tridgell had reverse-engineered the BitKeeper protocol in order to create Mercurial, which was a free and open-source alternative.
BitMover, the company that developed BitKeeper, claimed that Tridgell had violated the terms of service by reverse-engineering their software and creating a competing product. They also claimed that Tridgell had distributed unauthorized copies of BitKeeper.
Tridgell denied these claims, stating that he had only used publicly available information to create Mercurial and that he had not distributed any unauthorized copies of BitKeeper. He also stated that BitKeeper's license agreement allowed for reverse engineering for the purpose of interoperability with other software.
The dispute between Tridgell and BitMover led to the discontinuation of the free version of BitKeeper and the development of the Git version control system by Linus Torvalds and other members of the Linux community as a replacement for BitKeeper.
This dispute was more of a public disagreement on the use of open-source software, BitMover accused Tridgell of violating their TOS, but there isn't any evidence of him actually breaking any laws.