Microsoft fears that it might be affected by the same security flaw that could leave Linux systems vulnerable. The company has confirmed that the zlib software-compression library flaw could affect Office, Explorer, DirectX, Messenger, Windows XP and Front Page.

The applications contain code borrowed from the Linux compression library, making them vulnerable to a similar attack.

A Microsoft spokesman said it was not a forgone conclusion that any applications would be hit by the bug, but its security teams were investigating the situation.

The zlib library is used in almost every Linux and Unix system, and the so-called "double free" flaw in the library which was recently discovered may leave it open to attack.

The open-source compression project, Gzip, has identified more than 600 applications which use the zlib code, including some from Microsoft.

The fact that Redmond is investigating the problem has confirmed how much open sourced based code is within the company's products, according to analysts.

While Microsoft has never denied that it used open-source software, it forbids its programmers from using GNU General Public Licence code, which could force it to publish its own source code.