A key security feature of Windows Vista, User Account Control (UAC) is still nearly unusable, Symantec has said.

At a press presentation last week, Symantec vice president of engineering Rowan Trollope said Symantec's customers had found the feature so "chatty", that it was a burden on users, potentially creating new help-desk calls.

He said that personally he had found the feature so distracting he had finally turned it off - not a good sign for companies intending to use UAC to protect systems.

UAC allows administrators to create user accounts that have limited privileges, correcting what security experts perceive as a major weakness in previous versions of Windows. Previously, all Windows users were administrators, something nearly unheard of in the Linux/Unix world.

The change is designed to limit the damage malicious attacks can cause, and to put a damper on attacks that take over large numbers of systems. But it can only be effective if UAC is enabled on a large proportion of Windows systems.

The feature attracted criticism during the beta-testing process, from respected analysts among others, and Microsoft said it fine-tuned UAC.

Symantec does have a vested interest here - the company plans to sell products that smooth out UAC's alleged faults - but the company's findings could be evidence of spell additional headaches for system administrators considering Vista.

Symantec's idea is somewhat different; Trollope said the company is proposing to add an extra layer of "intelligence" on top of UAC which would make it easier to use. Such a plan will involve Microsoft's co-operation, Symantec acknowledged, but Microsoft security executives said the company was not yet aware of what Symantec has in mind.

Following Symantec's comments, Microsoft stood by its work. "If the user decides they do not want to run UAC and they would rather run a third-party solution that provides similar functionality, they do have the choice to disable it," Microsoft said in a statement.

Over recent months Microsoft has been moving toward bringing many basic security features under its own roof, providing its own firewall, antivirus and anti-spyware software, for example.

Symantec said users shouldn't get the idea that Vista no longer needs third-party security products - which, it admitted, would be a disaster for Symantec's own business.

So far, however, industry analysts have largely agreed with Symantec, saying Microsoft has yet to prove itself as a security provider, particularly at the enterprise level.