Even though the mainframe business is a declining industry, IBM still manages to keep its mainframe division lucrative. A key part in its business strategy is to lock consumers into IBM's mainframes - the software and hardware are tightly integrated, and the license does not allow you to run the operating system on anything else but IBM's System Z hardware. This means that you can't easily migrate or port software over to other platforms; nor can other hardware manufacturers build compatible hardware.
Enter Hercules, a System Z emulator. It's open source, and allows you to migrate your mainframe applications over to common hardware. Due to the licensing situation being rather murky, this was mostly a thing for enthusiasts. In fact, IBM has always been relatively positive about Hercules, and even offered documentation about it.
TurboHercules has changed this. The company employs a loophole in the licensing; it reads that users may transfer the software to another system in case of mainframe failure. TurboHercules markets itself as a disaster recovery tool using the Hercules open source emulator, and it would seem there's a market for that sort of thing. IBM isn't too happy about that.
It has now threatened to sue TurboHercules, stating that it violates a long "non-exhaustive" list of patents (issued or merely applied for) - two of which are also among the 500 patents IBM promised not to sue open source companies over. TurboHercules' founder had earlier sought to resolve the situation, and had asked IBM if they could come up with a solution for the licensing issue together.
Florian Mueller, European anti-software patent activist, notes the hypocrisy of the situation. "After years of pretending to be a friend of Free and Open Source Software, IBM now shows its true colors," Mueller writes, "IBM breaks the number one taboo of the FOSS community and shamelessly uses its patents against a well-respected FOSS project."
"This proves that IBM's love for free and open source software ends where its business interests begin," he added, "In market segments where IBM has nothing to lose, open source comes in handy and the developer community is courted and cherished. In an area in which IBM generates massive revenues (an estimated $25 billion annually just on mainframe software sales!), any weapon will be brought into position against open source. Even patents, which represent to open source what nuclear arms are in the physical world."
So, there you have it. It would indeed seem that IBM only caters to the open source crowd when it has nothing to lose - when push comes to shove, and money's to be had, IBM doesn't appear to be too keen on open source at all.