EXECUTIVE SUMMARY ON CPU USAGE:

By default, BFGMiner will NOT mine on CPUs unless it is explicitly compiled with
support and told to do so. CPU mining for bitcoin is generally considered to be
obsolete as it requires considerably more power per hash computed than either
GPU, FPGA or ASIC based mining. If you still wish to mine using CPUs you will
need to build a custom binary with support enabled (refer to the build notes in
README for further information).

The following CPU mining options are available:

--algo <arg>        Specify sha256 implementation for CPU mining:
        fastauto*       Quick benchmark at startup to pick a working algorithm
        auto            Benchmark at startup and pick fastest algorithm
        c               Linux kernel sha256, implemented in C
        4way            tcatm's 4-way SSE2 implementation
        via             VIA padlock implementation
        cryptopp        Crypto++ C/C++ implementation
        cryptopp_asm32  Crypto++ 32-bit assembler implementation
        sse2_32         SSE2 32 bit implementation for i386 machines
        sse2_64         SSE2 64 bit implementation for x86_64 machines
        sse4_64         SSE4.1 64 bit implementation for x86_64 machines
        altivec_4way    Altivec implementation for PowerPC G4 and G5 machines
--cpu-threads <arg> Number of miner CPU threads (default: -1)

CPU FAQ:

Q: What happened to CPU mining?
A: Being increasingly irrelevant for most users, and a maintenance issue, it is
no longer under active development and will not be supported unless someone
steps up to help maintain it. No binary builds supporting CPU mining will be
released for Windows but CPU mining can be built into BFGMiner when it is
compiled. For builds which do support CPU mining, it is still disabled by
default, and must be enabled using the -S cpu:auto option.

Q: So, should I even try CPU mining?
A: No, it honestly will waste more power and time than it is worth at this stage.
If you really wish to mine, you are better off getting a suitable ASIC instead.

Q: But, if the computers aren't mine and I'm not paying for the power?
A: If you are trying to use computers that aren't yours, you really should
reconsider. Attempting to mine with a large number of devices will often impact
negatively on many pools and will likely pay almost nothing due to the small
number of successful shares submitted. Apart from that, you will probably get
into trouble with someone down the track for misusing the computers.