The National Institute of Standards and Technology (NIST) is reported to have turned it back on Microsoft’s Vista, the third US government department in the last week to halt its adoption.

According to third-party sources broking the story, the department has yet to confirm the move, or give a firm reason as to why Vista has been deemed unsuitable for the agency.

NIST management are said to be due to discuss the matter during a special meeting on 10 April, while also mulling over the software’s security model in more detail.

Only Last week, two other US government agencies, the Department of Transport (DOT) and the Federal Aviation Authority (FAA) halted migration to Vista, in the FAA’s case because it wanted to examine the feasibility of using s rival system based on a Linux distribution running Google’s hosted Apps.

"Based on our initial analysis, there appears to be no compelling technical or business case for upgrading to these new Microsoft software products. Furthermore, there appears to be specific reasons not to upgrade," a memo said to have circulated within the DOT was reported as saying.

It is impossible to tell whether the recent string of setbacks from the US public sector augurs badly for Vista. It is likely, however, that managers will have been concerned that upgrading to Vista could impose significant upgrade costs, in addition to the cost of the software itself.

Upgrade scepticism has become more marked that it was during the early days of Windows XP, especially on the back of the move to browser and Internet-based business. Only a few months ago, one migration tools developer, Altiris, described the adoption process as taking up to 18 months, and as something not undertaken lightly. Some customers were only completing their move to XP, the company said.