W32Badtrans virus

Since we have norton corporate version antivirus we were able to stop this virus from the server by configuring the exchange server to scan every e-mail that comes in and goes out. But what I do not understand is we are still being hit by about 100 Badtrans virus on daily basis and I have to delet them from the qurantine several times a day. Is there something wrong with server or is it happening to everyone. I will appreciate any input in this matter.

Thanks.