Whirlpool is a hashing function created by Vincent Rijmen and Paulo Barreto, it uses a 52 bits hashing key, exactly like Sha-512which makes its using way slower than md5 or sha1 for instance. This relative slowness allows Whirlpool to be more secure against brute-force, which still remains possible with the actual hardware calculation power. Whirlpool implementation was also made to be slow, not as slow as slow hashes like for instance Bcrypt algorithm, but still enough to discourage bruteforce usage. Though a well thought bruteforce could succeed in cracking whirlpool long passwords.
Whirlpool produces a very long hash of 128 bytes, as the sha512, and so isn't very used for password storage in databases. However, this could be a good thing as you won't find a lot of lookup tables online, since this hashing function isn't widely used. As the others hashing functions, using a salt is advised to make the bruteforce way more complicated.