I'm not talking about openssl, PHP, or even the Linux kernel but all the above plus every other program or bit of code on a Linux system. It's vulnerable. It's hackable. It can be changed at will by anyone because the source is open and freely available (the definition of open source).
Windows code, on the other hand, is not open and available, therefore it's much safer.
Do you believe that open source programs are more vulnerable because their code is available, visible and accessible? Do you believe that the Windows operating system and Windows applications are more secure because the code isn't available to you and potential hackers?
You'd be right if you believe the first and wrong if you believe the second of those questions. Why?
While it's true that allowing someone to view your code, leaves it somewhat more vulnerable than if it were hidden--it is not true that hidden code is more secure. So, if it's more vulnerable, why all the hype about Linux and open source and why does anyone think it's better?
Because Linux is more secure. Say what???
It works like this: If your code is visible, hackers, crackers, and annoying tweakers can get in and perhaps find a security vulnerability and exploit it. It's also visible to the good guys who can fix those vulnerabilities--in fact, by the time you hear of a security vulnerability in the open source world, someone has already fixed it and posted the patch for all to download and use--many repositories pick up the fixes so that they can be installed automatically.
Alternatively, Windows vulnerabilities are often exploited worldwide at the cost of hours and hours of time, disrupted business, stolen credit card info, and compromise of critical data and systems. By the time a fix is available, the damage is done.
Ask anyone from the 2008 Black Hat Hacker's Conference where Mac OS X was hacked first, then Vista but Linux withstood all and emerged as the only OS that was not hacked.
Are you at risk? Yes, everyone is, but you're safer with Linux than with any other operating system. Keep that system up to date with yum, apt-get, smart or other automatic download, install and patch tools and sleep better at night.