Why does Awstats show links to my site from Pvt. Boxes?

Hello,
Recently i checked awstats and under Links from an external page (other web sites except search engines) i see following entries :
- http://www.robot-invasion.com/backtalk/privmsg.php 88 88
- http://naturalhealingcenter.com/discussion/privmsg.php 85 85
- http://www.smrt-tv.com/forum/privmsg.php 83 83
- http://www.easternecho.com/forums/privmsg.php 82 82
- http://www.e-inclusionsite.org/phpBB2/privmsg.php

I have never heard of those forums ever but i getting links from pvt boxes .

How can this be possible?

 

Maybe other people on those websites private someone and tell them about your website?

 

But so many . I wish i knew what they were pvt messaging (good or bad things )