On my mac (Lion), I know that curl is bing used by some unknown process to communicate with a server. Basically I installed little Snitch and find out that "somebody" is using curl periodically. ...
It is often helpful to be able to obtain a good cryptographic checksum of a file, e.g. the SHA-256 hash. This can be used to verify file integrity, so long as you have a reliable source for the hash. ...