not all aff programs are secure, and if you use one global password(for e-mail, hosting, aff. account), you can have big problems. I remember a few years ago a friend of mine sent me my password 
and some info about my earnings 
, he just clicked a link and obtained by incident for a few minutes admin rights to an affiliate program interface (not from CAP, an exotic one 
) to there player/ webmaster database, and because I used one password, he just checked my stats with other programs
So, use different passwords and change your e-mail password regularly.