Hmm, maybe market cap was the wrong comparison to make. The cryptocurrencies listed in that article are doing pretty well for themselves mining-wise. I suspect

Hmm, maybe market cap was the wrong comparison to make. The cryptocurrencies listed in that article are doing pretty well for themselves mining-wise. I suspect that there may be tiny cryptocurrencies traded on some exchanges that could be 51%-attacked by an individual for somewhere between $1,000 and $100,000 to double-spend some high-value transactions. Maybe it's unlikely for the numbers to line up to be profitable and sure enough to pull off, but if it does happen, then that cryptocurrency is toast as soon as someone notices.