Malware Distribution Project
In case you needed a comprehensive database of malware.
Malware Distribution Project (MD:Pro) offers developers of security systems and anti-malware products a vast collection of downloadable malware from a secure and reliable source, exclusively for the purposes of analysis, testing, research and development.
Bringing together for the first time a large back-catalogue of malware, computer underground related information and IT security resources under one project, this major new system also contains a large selection of undetected malware, along with an open, collaborative platform, where malware samples can be shared among its members. The database is constantly updated with new files, and maintained to keep it running at an optimum.
There are currently 271712 files in the system.
This isn’t free. You can subscribe at 1,250 euros for a month, or 13,500 euros a year. (There are cheaper packages with less comprehensive access.)
They claim to have a stringent vetting process, ensuring that only legitimate researchers have access to this database:
It should be noted that we are not a malware/VX distribution site, nor do we condone the public spreading and/or distribution of such information, hence we will be vetting our registrants stringently. We do appreciate that this puts a severe restriction on private (individual) malware researchers and enthusiasts with limited or no budget, but we do feel that providing free malware for public research is out of the scope of this project.
EDITED TO ADD (8/8): The hacker group Cult of the Dead Cow also has a malware repository, free and with looser access restrictions.