Unless you want to do it on a huge scale (see http://theverge.com/2013/12/2/5165428/bitcoin-mine-in-hong-k...), it's not.
You might want to look into mining litecoin (LTC), which might still be profitable and whose mining is CPU-based.
You might want to look into mining litecoin (LTC), which might still be profitable and whose mining is CPU-based.
Feeling smug that I'd be using spare, paid-for server cycles to make money, I looked up some expected earnings. (Warning: I'm an LTC noob, so may have plugged in bad assumptions), but even at 4khash/sec, I was looking at less than $3 a year
http://www.coinwarz.com/calculators/litecoin-mining-calculat...
I'd like to be proven wrong on this, of course. However, talking to a couple of people on IRC (hardly guaranteed 100% reliable info, but good enough for me) it seems that even LTC has moved to GPU mining being a lot more realistic than CPU mining)