I don't understand why you people are so paranoid about this. If you bothered to READ the description, it says right there what it is: Free dynamic dns domains for everyone. Choose a free name and get started within minutes.
This is yet another of those domain hosting sites that sadly got a bad reputation because of the abusers they all have to deal with.
Allows the transmission of: unlawful, harmful content of any kind or nature; aka: Malware
The short version:
3-a.net is only AN DYNAMIC DNS SERVICE! The bad rating isn't justified!
The long version:
I bet you've never called the main page of this domain: http://3-a.net/
And if you trust in me, you can read here something interesting: Free Dynamic DNS
And that says: The provider of the page don't affect the subdomains, that's only IP-Forwardings.
That says us: Everytime inform about the domain, and then you can start denoting the page as unsave!
Instead of accuse the whole domain to be bad, rate the actual subdomain as bad!
And as example I have a subdomain on this domain, and ther isn't any Malware, Virus etc. on it, it only mirrors my IP!