Incorrect Bandwidth Results ?

I hope this is a goog place to discuss this issue.
I have been using the Virtualmin Bandwidth Feature to calculate and provide some statistics to a customer about the bandwidth usage.
THe server we are using for hosting is a 100Mbit server and from a simple calculation it should not allow more than 1TB traffic/day.

100Mbit/s = 12.5MByte/s
12.5x60x60=45000MByte/hour or: 43,9GB/hour
43,9x24 = 1054,6 GB / day or ~1TB/day

The bandwidth logs are showing:
06/Jun/2009 1.54 TB
05/Jun/2009 2.46 TB
04/Jun/2009 1.36 TB
03/Jun/2009 1.53 TB
02/Jun/2009 2.10 TB

over 1TB.
Did I miss something in my calculations?