One simple way to ensure a file downloaded from the internet has not been changed in some way from the original is to check the file integrity by looking at the hash value.
A couple of the popular hash algorithms are MD5 and SHA1 and you will sometimes see these hash values listed on websites when you go to a software download page. An MD5 signature consists of 32 hex characters, and a SHA1 signature consists of 40 hex characters.
The File Checksum Integrity Verifier (FCIV) is a command-prompt utility that computes and verifies cryptographic hash values of files. FCIV can compute MD5 or SHA-1 cryptographic hash values. These values can be displayed on the screen or saved in an XML file database for later use and verification.
this tool is available for download from the Microsoft Download Center