Most good antivirus programs should be able to detect Back Orifice. Some will also remove it for you. The information available on the Internet about Back Orifice tends to be out of date, I found as I did some checking. These sites have some relevant information which you should find useful: http://www.sg1.net/security/bomain.htm
http://www.nwinternet.com/~pchelp/bo/morefindBO.htm As you'll see, there are several programs which can assist you in removing this program. Also, instructions on how to look for it manually are indicated.