IBM customers are becoming increasingly frustrated at the lack of comment from the company since SCO revoked its AIX Unix licence.

Since 13 June all of IBM's AIX customers have been running unlicensed software after SCO pulled IBM's rights to use or distribute the operating system. IBM rejects this claim.

The UK IBM Computer Users' Association has now written to IBM asking that it provide "assurances that IBM's customers and our members will not suffer any financial or operational loss from this dispute".

The letter added: "We would hope that IBM would compensate [customers] for any inconvenience caused to them."

IBM has remained practically silent about SCO's $3bn lawsuit, making little comment other than to say: "IBM's Unix licence is irrevocable, perpetual and fully paid up.

"It cannot be terminated. IBM will defend itself vigorously. IBM will stand behind our products and our customers."

The company has yet to respond to the user group's letter, which was sent at the beginning of last week. The user group has traditionally had a strong relationship with IBM.

"IBM isn't enhancing its position in this," said Ray Titcombe, chairman of the UK IBM Computer Users' Association.

"I'd have liked to see them be a great deal more supportive to their customer base; to go that extra mile that says 'We are that confident that we will act as guarantors.'"

The user group is concerned that by saying nothing, IBM may be damaging future business among customers thinking of buying new, or upgrading current, systems.

But Gary Barnett, principal consultant at analyst Ovum, insisted that there was little danger of harm coming to IBM users.

"Realistically, the likelihood of IBM's [AIX] customers being sued by SCO is next to zero. The absolute worst case scenario is for them to have to pay a licence fee, and this is next door to zero," he said.

"There is no need for anyone to run to IBM for indemnification. In a fight between a terrier and an Irish wolfhound, it's the yappy little dog that makes the most noise. But that doesn't mean it will win the fight."