The SCO Group has finally laid down exactly where it believes its copyright has been infringed in IBM code.

The crusading Unix vendor, which has drawn criticism and mockery for attempting to stake a claim over open-source OS Linux, says it now has emails that prove IBM violated SCO licensing terms in the latest version of its AIX operating system.

IBM used Unix code in AIX 5L that SCO had licensed to IBM for "Project Monterey" - an effort to build a version of Unix for Intel's Itanium processor but without possessing a separate licence, SCO has claimed.

Forbes.com first reported the AIX allegations, attributing them to remarks made by SCO head Darl McBride on the sidelines of the company's annual user conference. A SCO representative has since declined to comment on the licensing charges and an IBM spokesman did not immediately return a call seeking comment.

McBride did threaten future revelations during his keynote speech, saying: "Keep your eye on the [court] filings. Over the coming year, one of the things that you're going to see is that Big Blue has got big problems." The SCO spokesman reiterated this line: "You can expect to see more on the issue in future legal filings."

IBM and SCO have tangled for over a year on the alleged copyright infringement, which SCO says has found its way in Linux. The new allegations against AIX were discovered as part of the exchange of documents in that ongoing legal dispute.

SCO has been challenged several times by IBM to state exactly where it feels the infringement has occurred. SCO's response has been to ask for more IBM code to be disclosed to it.