On October the 18th, Valves Digital PC Platform, STEAM hit an all time new milestone when over 10 million users were logged on at the same time. Stats from STEAMS official stat page shows a peak of 10,761,566 Users Online on the 18th of this month. The last record was 10 million which occured in June with the previous high reaching 9.5m Online Users in May of this year.
Based on current player count the top five STEAM games currently are as follows,
Below is a graph of the STEAM Stats, showing the record high.