One day I was asked to learn passwords for 7 hashes. First I tried the internet services but the only positive result was adding hashes to databases for bruting later. Within 3 days four hashes were known. There was regularity according to which first symbols of passwords were known. Besides it the alphabet and the length were also known. It was time for mask attack. No rainbow tables (because of the size) or dictionaries (because words were not usual) were helpful. I don't possess a good video card for using CUDA so I referred to the tools which are able to perform mask attack on CPU. But the speed was very low, I could wait for weeks for all the hashes to be cracked. So I took a look at the world's fast MD5 cracker. It's nearly 12 times faster than other tools on CPU. But it can only bruteforce hashes without any other modes (no mask attack in such a case). I modified it, so now it knew about the first known symbol and with the help of this program I got unknown hashes practically in no time. If the process is interesting for you and you want to know perspectives of this way please refer to rather detailed attachment. It is published with the permission of the author of this tool.

By the way it's interesting to read your replies to the subject. What do you think about it?