Defamatory Internet posts

I knew I would find something I needed if I came here... Okay you people...this is a US problem...so does anyone know of what can be done legally on internet harrasment?... this is not me...but I am close to the person going through it... they have Yahoo lists and have been attacked viciously and accused of stealing things from other developers of similar items and selling as their own...I know this person is not guilty of this...they had a yahoo store and the opponents 3 times in a year complained to yahoo and had them shut down...now they have gotten smart and gone to an independent provider... so that part is covered...but they are still being viciously attacked via different lists about this...one person has emailed copies of an edited IM message between my friend and them and sent it out to THOUSANDS...I got one...and it is obvious parts were left out... they still email my friend daily with repeated threats of legal action if they do not "fess" up that they are guilty...it is ruining this persons home life and marriage and health...this person IS NOT GUILTY...why confess?... I want to help as I am in the same line of business and this person was there for me and many others when I started out...they have given till they can give no more... the ones against my friend have the same kind of business but not nearly as lucrative...and they want my friend OUT Of the busines...and my friend is not the only one they have done this to....SO what can she do leagally to stop this harrasment?...

 

okay this is a start...I am personally going to complain to Yahoo that I was spammed by them using email addresses they gleaned from the different groups... this has got to stop... thank you for your quick response...