Although Linux has been termed as a secure OS, kernel level malicious attacks can still happen. This is not the first time that the Vendor-Sec distributor security list has been compromised. It happened earlier in 2005 also. Is Linux just as vulnerable as any of the other available operating systems, is a point of discussion.
At the root of it, let us be sure of one thing, practices of the users clearly define the vulnerability of any operating system. We can only say that compared to the Windows platform, the Linux platform has suffered really very minimal attacks. What matters most is the security standards, or rather the lack of it, when defining how secure an operating system can be. Linux is neither intrusion proof, and is definitely not hacker proof. Linux is only extremely difficult for unauthorized entrants to break into.
Linux comes with a whole set of repositories as a part of the standard. If you are careful enough, not installing anything outside of the standard set of repositories, and you are quite safe. Regular updating is a must. The only difference between Linux and others is that the response time for the open source community, patching up of security holes, is extremely fast. Consider this the real beauty of Linux. Besides patching of holes, updates and fixes are rapidly sent out, minimizing whatever damage has been caused, very quickly.
Principally, being a multi-user networked system, the Linux is basically better on security. Linux was basically built to deal with potentially hostile environment. Only last week we saw the Ubuntu and their Linux kernel problems affecting quite a few versions of Linux.
It is absolutely essential that a very careful configuration of your firewall is done. Activating various filters and not allowing remote administration features and tools, can make the Linux environment safe and secure.