> more unique That makes it sound like you're thinking that the chances for a conflict (same hash value) depend just on the size of the hash value. But it's wo

> more unique That makes it sound like you're thinking that the chances for a conflict (same hash value) depend just on the size of the hash value. But it's worse than that, thanks to algorithmic insights, inputs that produce the same hash value can be found more cheaply than just by chance. Also, they can be found so cheaply that it's computationally trivial to do even for an individual [1]. Thus anyone who can change what data you receive, can trivially also make it hash to the same MD5. (I haven't checked whether publicly available software exists to generate conflicting files that are also, for example, valid gzip files, but I surely expect that an entity like the NSA (and perhaps blackhats, too) can create such software on their own.) [1] "produce a collision for two inputs with specified prefixes within hours, using off-the-shelf computing hardware": https://en.wikipedia.org/wiki/Md5#Security https://en.wikipedia.org/wiki/Md5#Security Yes, there are many sites that still tell users to check MD5 hashes. I think it's evident that those are totally worthless for some years now. Worse, it may be giving some people a false sense of security. OTOH those places might give those who do know a hint that perhaps the authors or distributors don't know about security. (Sorry for the harsh words...)