After you've downloaded the file, you can use an MD5 checksum tool to hash the file and see if the checksum matches the one on the web page. If they are different, then you know that the file you downloaded is not the same as the one that the web site intended for you (either it was damaged during download, or someone has tampered with it).
It's not just for downloading files over the Internet. Copying large files over a slow WAN link can sometimes cause corruption. This is why I wrote this tool. I copied a 5GB VMware OVF template from the US to China, which took a very long time. When the copy finished and I tried to import the template, it failed with a checksum error. So I wrote the MD5 checksum viewer and saw that the checksum didn't match.
The MD5 checksum viewer (md5Check.exe) is a simple to use GUI tool for Windows. Just launch the tool, browse to the file you want to check, then click Get Hash. The tool will read the file (which might take a few seconds for large files) and display the hash.
Requirements: Any version of Microsoft Windows with .Net Framework v2.0 or higher.
Obligatory Disclaimer: As with any software downloaded from the Internet, please use md5Check.zip at your own risk. ITAdminTools.com makes no claim as to the safety or usefulness of the software, and no warranty nor liability is expressed or implied.
Download md5Check.zip here - courtesy of ITAdminTools.com