sha1sum is a computer program which calculates and verifies SHA-1 hashes. It is commonly used to verify the integrity of files. It (or a variant) is installed by default in most Unix-like operating systems, including Mac OS X. Variants include shasum (which permits SHA1 through SHA512 hash functions to be selected manually) and sha224sum, sha256sum, sha384sum and sha512sum, which use a specific larger hash function than SHA-1. Versions for Microsoft Windows also exist.
Some cryptographical weaknesses have been found in SHA1.[citation needed] However, sha1sum is still usable for general-purpose file checksumming, and is widely considered more secure than MD5 or a CRC.[citation needed]