can somebody make the calcs if it is feasible to have mined 25k btc from december 2010 as he said he started?
would he need many many suspicious gigahashes?
Let's calculate.
Blocks are averaged to be 1 Block every 10 minutes (or 6 blocks an hour). This is controlled by difficulty. So, as blocks are found more rapidly, the difficulty adjusts to bring us back to the average. For the sake of argument, we'll say it's 6 / hour.
6 blocks / hour = 144 blocks / day
144 blocks / day * 50 BTC / block = 7,200 BTC / day
25,000 BTC / (7,200 / day) = 3.47 days to accumulate 25,000 BTC
However, the odds of finding every block for 3.5 days is pretty small, unless you're the only one mining.
So, let's say he only found 10% of the blocks (14 blocks / day). That means 10x the length of time run, so 35 days.
Easily achievable from December 2010 - March 2011 (when things started getting crazy), even if he was only finding 3% of the blocks.