On Dec. 15, a Russian programmer posted a description of a flaw that makes it possible to increase a person's privileges on all of the company's recent operating systems, including Vista.
Over the weekend a Silicon Valley computer security firm said it had notified Microsoft that it had also found that flaw, as well as five other vulnerabilities, including one serious error in the software code underlying the company's new Internet Explorer 7 browser.
The browser flaw is particularly troubling because it potentially means that Web users can become infected with malicious software simply by visiting a booby-trapped site. That would make it possible for an attacker to inject rogue software into the Vista-based computer, according to executives at Determina, a company based in Redwood City, Calif., that sells software intended to protect against operating system and other vulnerabilities.
Determina is part of a small industry of companies that routinely pore over the technical details of software applications and operating systems looking for flaws. When flaws in Microsoft products are found they are reported to the software maker, which then produces fixes called patches. Microsoft has built technology into its recent operating systems that makes it possible for the company to fix its software automatically via the Internet.
Despite Microsoft assertions about the improved reliability of Vista, many in the industry are taking a wait-and-see approach. Microsoft's previous operating system, Windows XP, required two "service packs" issued over a number of years to substantially improve security, and new flaws are still routinely discovered by outside researchers.
On Friday, a Microsoft executive posted a comment on a company security information Web site stating the Microsoft was "closely monitoring" the vulnerability described by the Russian Web site. It permits the privileges of a standard user account in Vista and other versions of Windows to be increased, permitting control of all of the operations of the computer. In Unix and modern Windows systems, people are restricted in the functions they can perform, and complete power is restricted to certain administrative accounts.
"Currently we have not observed any public exploitation or attack activity regarding this issue," wrote Mike Reavey, operations manager of the Microsoft Security Response Center. "While I know this is a vulnerability that impacts Windows Vista, I still have every confidence that Windows Vista is our most secure platform to date."
Secunia, another security company, gave the same flaw a "less critical" rating in an advisory posted Friday. On Saturday, Nicole Miller, a Microsoft spokeswoman, said the company is also investigating the reported browser flaw and that it was not aware of any attacks attempting to use the vulnerability.
Microsoft has spent millions, and it is counting on Vista to help turn the tide against a wave of software attacks now plaguing Windows-based computers.
. Despite an almost four-and-half-year campaign on the part of the company, and the best efforts of the computer security industry, the threat from harmful computer software continues to grow. Criminal attacks now range from programs that steal information from home and corporate PCs to growing armies of slave computers that are wreaking havoc on the commercial Internet.
Although, has been extensively tested, it is only now being exposed to the challenges of the open Internet.
"I don't think people should become complacent," said Nand Mulchandani, a vice president at Determina. "When vendors say a program has been completely rewritten, it doesn't mean that it's more secure from the get-go. My expectation is we will see a whole rash of Vista bugs show up in six months or a year."
The Determina executives said that by itself, the browser flaw that was reported to Microsoft could permit damage like the theft of password information and the attack of other computers.
However, one of the principal security advances of Internet Explorer 7 is a software "sandbox" that is intended to limit damage even if a malicious program is able to subvert the operation of the browser. That should limit the ability of any attacker to reach other parts of the Vista operating system, or to overwrite files.
However, when coupled with the ability of the first flaw that permits the change in account privileges, it might then be possible to circumvent the sandbox controls, said Alexander Sotirov, a Determina security researcher. In that case it would make it possible to alter files and potentially permanently infect a target computer. This kind of attack has yet to be proved, he acknowledged.
The Determina researchers said they had notified Microsoft of four other flaws they had discovered, including a bug that would make it possible for an attacker to repeatedly disable a Microsoft Exchange mail server simply by sending the program an infected e-mail message.
Last week, the chief technology officer of Trend Micro, a computer security firm in Tokyo, told several computer news Web sites that he had . Over the weekend a spokesman for Trend Micro said that the company had not obtained the information, and as a result could not confirm the authenticity of the offer.
Many computer security companies say that there is a lively underground market for information that would permit attackers to break in to systems via the Internet.