The SCO Group's case against IBM over alleged Unix contract and copyright violations took another twist on Friday when SCO returned to court with amended allegations and increased its damages claim to $5bn.

SCO and IBM's return to court was intended to confirm that SCO had complied with IBM's request for specific evidence in the discovery process. But, just before the hearing, SCO altered its claim.

Last June, SCO revoked IBM's AIX (Unix) licence, although IBM claimed that it was irrevocable and ignored the action. SCO took this move on the ground that IBM had revealed trade secrets.

SCO has now dropped this allegation and is instead claiming breach of copyright, accusing Big Blue of making parts of Unix variants AIX and Dynix (Sequent's flavour of Unix, which it acquired in 1997) available in Linux.

The amended suit also alleges that IBM encouraged Novell, from which SCO acquired the Unix licence rights, to make copyright counterclaims against SCO. It has added $1bn for each new claim.

But presiding US magistrate Judge Brooke Wells has yet to rule on whether SCO can introduce the new claims, announcing that she will do so in writing within the next week.

Meanwhile, the two sides squabbled on Friday over whether SCO has provided the information to IBM mandated by an earlier court ruling.

On 12 January SCO stated that it had complied, but the confirmation hearing was put back from 23 January to 6 February after IBM stated that SCO had not fully complied with the court order to provide proof of its allegations.

On Friday, IBM argued again that SCO had not provided full, complete and detailed evidence.

But SCO's lawyer, Mark Heise, claimed that the company had given full details of the improper contributions made by IBM to Linux, represented in some 17 lines of code.

In order to provide the line-by-line evidence IBM is demanding, SCO argues that it needs IBM to provide AIX and Dynix operating system code, which coincidentally SCO is demanding from IBM in the next phase of the discovery process.