Microsoft has acknowledged a flaw in its popular Internet browser that could let hackers steal "cookies", the sensitive files used by e-commerce sites to track and conduct business with customers online, according to the Wall Street Journal yesterday.

The browser flaw is worrying not only because it could give hackers relatively easy access to sensitive data, but also because it could affect such a large group. According to the article, roughly two-thirds of Web users are reliant on the two most recent versions of Microsoft's Web browser, "It's definitely a vulnerability," said Mr Steve Culp, a top security official at Microsoft, which has vowed to repair the problem soon.