Many download websites and developers display a so called MD5 hash code of the application that you want to download on their website which can be used to verify the integrity and authenticity of it. This can be done by comparing the MD5 hash code of the downloaded file with the one on the homepage where you did download it from.
Check MD5 Hashes
MD5 (Message-Digest algorithm 5) can be used as a way of checking that a computer file has not been maliciously or accidentally altered. To put it simple, it works like a fingerprint. So, nowadays most of websites includes this information to their software, which looks like this:

