I set up a new mining computer Thursday night that has a hash rate of 640000 khash/s. I also have my main system mining at a rate of 320000 khash/s. Based on the probabilities provided via http://www.alloscomp.com/bitcoin/calculator.php
, on average, I should see a block every 1.21 days (assuming 900 Mhash/s), and I should have a 95% chance of seeing a block in 3.625 days. Since I've yet to see a block on either of these systems I'm beginning to worry that something has been hacked or there is some other problem.
At what point should I assume there is a problem and clean off the systems and re-start? Based on the 50% time, I estimate a 99% chance for 6 days of mining, which would be Wednesday morning. The odds of 6 days of mining at 900 Mhash/s without a block is 1/100.
Anyone have any ideas on what to look for regarding a hack?
Don't worry man, I know the feeling and it is perfectly normal. The same way sometimes you may see many blocks generated within a short period of time, sometimes you won't see any of them for a while (even above 95% - I have experienced that myself a few times).
Still, maybe there is something wrong with your miners.