Google security have announced that they have a working collision attack
against the SHA-1 hash:
It's highly recommended to move to sha-256 where doable.
Note that MediaWiki uses sha-1 in a number of places; in some such as
revision hashes it's advisory for tools only, but in other places like
deleted files (filearchive table) we use it for addressing, and should
consider steps to mitigate attacks swapping in alternate files during