I have a Ubuntu installation running in VirtualBox. I have made a few modifications to it (some kernel modules and startup scripts) that I hope would make it very secure. Is there anyway I can test some malware on it? The virtual machine is versioned, so I can revert to a clean state easily.
Do you mean you want to get sample malware? According to the book Advanced Malware Analysis, there are a few public resource to get those like:
malshare.com Open Malware (http://gtisc.gatech.edu/) malwareblacklist.com
You can find out more in that book.