Dangerous documents.

According to the British Broadcasting Corp., the U.K. government recently decided to abandon Microsoft Word for documents that become public and instead use documents created with Adobe Acrobat, which uses the portable data format (PDF).

Why? Because metadata, typically considered helpful, may be too helpful to some. A document created, opened, or saved in Microsoft Word may contain content that the author might not want to share with others when the document is distributed electronically. This metadata may include names and user names of authors, companies, network server, or hard drive where the document was saved, file properties, document revisions, template information, hidden or previously deleted text, and e-mail headers, server, and printer information.

Computer experts say information tends to leak when users are working with a document that has had a number of revisions or several authors. A function in many versions of Microsoft Office programs, including Word, Excel, and PowerPoint, allows data fragments from other versions a user previously deleted or was working on at the same time to be hidden in any document he or she saves.

With the right tools, this hidden data can be extracted easily. U.K. computer researcher Simon Byers conducted a survey of Word documents available on the Internet and found that many contain sensitive information. He gathered about 100,000 Word documents from various Web sites and every one contained hidden information.

In a research paper, Byers wrote that half the documents collected had up to 50 hidden words, a third up to 500 words hidden, and 10 percent had more than 500 words concealed within them. The hidden text revealed the names of document authors, their relationship to each other, and earlier versions of the documents. It occasionally revealed personal information such as Social Security numbers and data about the internal network the document traveled through.

For those worried about leaky Word documents, Byers suggests using a different word processing program, employing utility programs that scrub information from Word documents, or following Microsoft's advice about how to make documents safer. For more information, visit http://support.microsoft.com.