spam-resistant return address for newsgroups

i'm receiving a lot of spam when i post to ng's - some of it containing
dangerous viruses (swen32, eg). being less naive now, i want to change my
return email address to be bot-resistant - something like
nweissma@SHOOTcovad.net.

i thought i accomplished this some time ago, but apparently i was not as
successful as i thought. please apprise me of the correct procedure.

thanks.