Microsoft has released new software that it said would help protect computers from Office 2003 files containing malicious software code.

Both tools, which were announced earlier this month, are designed to help defend against Office "zero-day" attacks, which take advantage of vulnerabilities before a patch is released by Microsoft. These type of attacks have become more common in recent months as attackers look for holes in Office to penetrate corporate networks.

The first tool to defend against these attacks, called Microsoft Office Isolated Conversion Environment (MOICE), has been designed to protect users running Office 2003 and 2007 Office.

MOICE works by converting Office 2003 binary files to the Office Open XML format used by 2007 Office, blocking out malicious code in the process. Importantly, this conversion takes place inside an "isolated environment," which Microsoft said prevents malicious code from running on the computer.

The second tool, called File Block Functionality for Microsoft Office 2003 and the 2007 Microsoft Office system, gives system administrators the ability to define which file types can and cannot be opened by users. This gives administrators the ability to block access to certain files when a specific threat arises, Microsoft said.

Microsoft detailed MOICE and File Blocker in a security advisory, recommending that both tools be used to protect against malicious Office documents. The advisory includes links to the necessary files and detailed installation instructions.