How I knew how the passwords were hashed?

Hashes have a length of 40 characters (hex encoded), so I guessed it's SHA1

Source code from file: login.php

$form_password_hash = forum_hash($form_password, $salt);

function: forum_hash()

Source code from file: functions.php

							function forum_hash($str, $salt){

$return = ($hook = get_hook('fn_forum_hash_start')) ? eval($hook) : null;
if ($return != null)
	return $return;

return sha1($salt.sha1($str));
}
						

So passwords were hashed by schema:

SHA1(SALT+SHA1(password))

What is salt?

In cryptography, a salt is random data that is used as an additional input to a one-way function that "hashes" a password or passphrase.

How I break the passwords?

I used dictionary method

Main loop

					while (dictionary.ready() && existsNotBreakHash) {
	String word = dictionary.readWord();
	String sha1 = DigestUtils.sha1Hex(word);
	users.parallelStream().forEach((user)->{
		String encodeSaltSha1 = DigestUtils.sha1Hex(user.getSalt().concat(sha1));
		if (user.getPassword().equals(encodeSaltSha1)) {
			database.updateUserData(user, word);
		}
	});
}
				

Apache Commons Codec is used to generate the digests.

Results

Dictionary: 4GB (320*106 words)

Hashes to crack: ~2000

Hashes cracked: 103

Digests generated: 40*109

Time: 40h

CPU: Intel® Core™ i7-4810MQ 2.8 GHz

CPU usage: 100%

Example