To verify the integrity of your downloads you can find the checksums of our files at https://sourceforge.net/projects/buck-security/files/buck-security/ by clicking on the "i" icon next to the files.
MD5 is a cryptographic hash function with a 128-bit hash value commonly used to check the integrity of files.
Unfortunately there have been found several vulnerabilities in MD5 and also in SHA-1 which is sometimes recommendend as an alternative.
To find out more about these vulnerabilities Wikipedia is a good starting point for both MD5 and SHA-1.
Crypthography Superman Bruce Schneier also has a lot of facts on his site (search for "MD5" or "SHA-1" there).
A new hash algorithms is already in the pipe, you can find more informations at this site of the National Institute of Standards and Technology (NIST) which started a public competition to find the new SHA-3 algorithm.
But this process can take a while. Meanwhile it is recommended to use SHA-224, SHA-256, SHA-384 or SHA-512 instead of MD5 and SHA-1. Buck Security therefor also provides the SHA-256 checksums to check the integrity of the program. And also in the buck-security program itself SHA-256 is used when we create the checksums of important system programs.