All versions of the Microsoft Windows Operating System have had flaws discovered that would allow an attacker to break into a computer running Windows.  Microsoft frequently releases patches to update Windows, fixing the flaws, and making the computer more secure.

To patch your computer, click on "Windows Update" under the "Tools" menu of Internet Explorer.  It will open a window of Microsoft information, and you can click on the "Scan for Updates" link to initiate a search to determine what patches your computer needs.  Microsoft classifies its patches into a few different categories.  Some of the other categories may be useful to you, but to secure your computer, you must install all patches listed in the "Critical Updates and Service Packs" area.  It will download and install the patches, sometimes requiring you to reboot for the changes to take effect.  You can also find Windows Update at http://windowsupdate.microsoft.com.