DENIC is only responsible for the registration of domains directly under the Top Level Domain (TLD) .de. It is the domain holders who are responsible for their individual domains as well as the contents and services that are available through them or processed by them. You can only get an IP address in combination with Internet access from an Internet Service Provider (ISP). ISPs have number blocks assigned to them by the Regional Internet Registries (RIRs).
It is thus never possible for DENIC to be able to find out directly who is the source of spam mails or hacker attacks. DENIC is not able to block them, nor is it able to take any further steps.
There are certain means available to you if you want to launch your own search: If the source of trouble is a domain or subdomain under the Top Level Domain .de, you can use our whois query to establish the name of the domain holder and/or the administrative contact (admin-c).
You should then contact the domain holder and/or admin-c by letter, fax or e-mail and tell them what it is that concerns you. If the domain holder or admin-c is to find out which individual is responsible and possibly to take further steps, they are going to need full and precise information from you (mail header and/or exact time/time zone, domain, IP address, and so on).
If the source is a domain or subdomain under another country code Top Level Domain (ccTLD), that is where you should go for your whois search. IANA can tell you which Registries are responsible for all the world's ccTLDs.
If the source is a domain or subdomain under a generic Top Level Domain (gTLD), such as .com or .info, you should use the Internic whois search to obtain information about the domain holder.
If the source is an IP address (such as: 192.168.111.80), the first thing you must know is that the IP address space is currently being administered by four different organizations around the world. You can find out the name of the address holder and/or administrative contact (admin-c) by making whois searches in the appropriate network:
RIPE NCC (Europea): http://www.ripe.net/perl/whois
ARIN (America): http://www.arin.net/whois/index.html
APNIC (Asia): http://www.apnic.net/apnic-bin/whois.pl
LACNIC (Latin America and Caribbean): http://lacnic.net/cgi-bin/lacnic/whois
AFRINIC (Africa and Indian Ocean): http://www.afrinic.net/cgi-bin/whois
IANA's website includes a list of which IP blocks have been assigned to whom. In many cases that will already tell you which of the above-mentioned organizations you will need to contact. To give an example, addresses starting with 193, 194 or 195 belong to the zone administered by RIPE NCC. There are, however, other IP addresses, such as those starting with a number between 128 and 172 where it is unfortunately not so easy to establish their assignment, since they have been divided into part blocks and assigned to various RIRs.
You should next contact the IP network owner or admin-c and tell them what the problem is. If they are to be able to use their log file to find the correct contact and possibly to take other steps, they are going to need full and precise information from you (mail header and/or exact time/time zone, domain, IP address, and so on).
For reasons of data protection and/or the legitimate interests of others, it is initially left to the discretion of the particular provider or domain holder whether or not they disclose the precise contact data to you or whether they take corresponding measures directly themselves. If you have suffered any actual loss or damage, it might be advisable to seek professional legal guidance.