Millions of people using Microsoft's Office and Internet Explorer programs are at risk from security holes that could allow malicious hackers to change files on their computers.

The vulnerable programs include Microsoft Office 2000, Office XP, Money 2002, Money 2003, Project 2002 as well as software used on internet servers.

The world's leading software maker has advised computer users to close the critical holes by downloading software patches from its website.

The flaws are the latest headaches for Microsoft, which launched a "trustworthy computing" campaign earlier this year to improve the security of all of its software.

Millions of users

The security flaws in the software means an attacker could use e-mail or a webpage to send commands to a user's computer to view files, run programs, alter data and even reformat the hard drive.

Gates: Emphasis on secure software

One of the products affected, Office, is used by around 100 million people to write documents and crunch numbers and is a major source of revenue for Microsoft.

But the company said it was not aware of any specific security breaches or the amount of any potential damage that might have occurred due to these latest flaws.

"Microsoft is committed to keeping customers' information safe," said Microsoft Security Program Manager Christopher Budd in an e-mail.

Closing loopholes

Since Microsoft boss Bill Gates launched his company's trustworthy computing initiative in January, the software giant has issued at least 30 security bulletins for flaws in its software.

Earlier this month it investigated reports that its browser has a loophole that could expose a computer user's name, passwords and credit card numbers.

Security experts say that Microsoft has become far more open about warning people about security failings.

"They are becoming very good at telling people when there are problems and that is a good thing," said Graham Cluley, senior technology consultant at anti-virus firm Sophos.

"But one of the really disturbing things is that people don't patch their software," he said, urging users to download the latest updates from Microsoft's Windows Update site.