This happens if you have told the installer to install the VPOP3 Antivirus option. The antivirus program starts when VPOP3 starts so that it is there in case you turn it on.
If you do not want it any more:
- Stop VPOP3
- Delete the VPOP3\plugins\vpop3av.vlb file and the VPOP3\plugins\vpop3av folder
- Restart VPOP3