The situation changed fundamentally in Excel 2007, where the modern AES algorithm with a key of 128 bits started being used for decryption, and a 50,000-fold use of the hash function SHA1 reduced the speed of brute-force attacks down to hundreds of passwords per second.
The more powerful RainbowCrack program was later developed that can generate and use rainbow tables for a variety of character sets and hashing algorithms, including LM hash, MD5, SHA1, etc..
RFC 4635 was circulated to allow RFC 3174 Secure Hash Algorithm (SHA1) hashing and FIPS PUB 180-2 SHA-2 hashing to replace MD5.