Now, we know for sure that Microsoft has seen its own source code and so have proven computer criminals. It is utterly insecure by design. Just ditch it. Buy, copy or download Linux and try it out on the desktop. Any mistakes you make can damage your system.
Viruses can spread unchecked.
A well-configured Linux machine is much more difficult to compromise with a virus or a Trojan. Block executable content at your mail server. Install virus scanners on your Windows PCs and your servers. But realize that they will not catch viruses which aren't in their database, so using a virus scanner mostly supports the virus-scanning industry and slows down your computer without buying you all that much protection. Oh, and don't disable the scanner as Microsoft employees were conjectured to have done the Trojan which infected Microsoft was old and well-known.