Microsoft finally rolled its Vista operating system out the door Tuesday, billing it as its most secure operating system ever, but what are the security features that will really matter to enterprise users?

To answer this question, IDG News Service asked Russ Humphries, a senior program manager with the Vista security team, to list the three Vista features that will have the biggest effect. Here's his list:

1) UAC (user account control)

Before Vista, Windows automatically gave users too much power over their systems, Microsoft has said.

With UAC, Windows will require a few extra steps before the user can do things such as install new programs. The feature will make it much easier for corporate administrators to lock down desktops and prevent users, or malicious programs, from messing around with the system or installing unauthorized software.

UAC has been one of Vista's most controversial features with early testers complaining that they were overwhelmed with pop-up messages warning them about every little change they made to the system. But these warnings will not slow down most enterprise users because they won't be installing device drivers or software, Humphries said. "Most corporate users are going to get a corporate image that will have all their applications already installed on the image," he said.

2) Windows Defender

With Vista, Microsoft has built a defense against pop-up ads and unwanted spyware right into the operating system. Although Defender has been criticized for not being as effective as commercial products, the fact that it will be so widely deployed is bound to improve things. "Adware is a huge annoyance, a security risk, and a bit of a machine hog, " Humphries said. "This has benefits for home users, small and medium-sized enterprises, and even large organizations."

3) BitLocker

There have been more than 100 million U.S. victims of data breaches over the past two years, according to Privacy Rights Clearinghouse. BitLocker aims to prevent the next 100 million from getting hit quite so quickly by giving corporate users a way to encrypt and password-protect their data. With BitLocker encrypting Vista's data, a stolen PC doesn't turn into a front-page data breach story, as was the case with the U.S. Department of Veterans Affairs last year.

BitLocker can also ensure that the operating system hasn't been tampered with at boot-up time, but customers seem to particularly appreciate the fact that it will help keep their companies out of the newspapers every time a laptop is lost. "I've had a lot of thank-yous from our customers," Humphries said.