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As noted above, Word®/Excel® 97/2000 used to encrypt files with RC4 if File open protection was used. The simplest way to break the password is running brute-force and dictionary attacks; however, these methods work well only on short and simple passwords. Longer passwords take considerably more time to break. For example, a 10-characters password containing small letters, capital letters and digits has the following number of possible combinations:

(26 + 26 + 10) ^ 10 = 839,299,365,868,340,224

AOPB does not attack passwords. Instead, it targets RC4 40-bit keys, which only have the following number of possible combinations:

2 ^ 40 = 1,099,511,627,776

Instead of trying all possible passwords, AOPB tries all possible encryption keys. Once the key is found, it decrypts the document, so the password is no longer required. The decryption is not instant, but the recovery time is very reasonable (usually, a matter of hours). Moreover, this method provides 100% success rate regardless the password length.

AOPB Enterprise Edition can use pre-computed hash tables that reduce the key search time to several minutes.