There is a Bash shell bug that is blowing up on the security webs as it could be exploited like heartbeat. It isn't fully fixed yet either, so it's worth keeping an eye on if you run GNU/Linux.

http://askubuntu.com/questions/528101/what-is-the-cve-2014-6271-bash-vulnerability-and-how-do-i-fix-it

Am I vulnerable?

Edit for the time being: You are. No complete public fix has been posted yet, for the new CVE (CVE-2014-769). The instructions I give below are only sufficient to close off part of the vulnerability.

There is an easy check. Open a terminal and paste the following:

env x='() { :;}; echo vulnerable' bash -c 'echo hello'

It simply sets the environment variable called x to the value '() { :;}; echo vulnerable'. It then invokes bash asking it to echo back the word hello. The value of x that is set is a function definition that should do nothing. However, it is crafted to try to run 'echo vulnerable' at parsing of environment at bash start-up, which just prints vulnerable to standard out.

If you are not vulnerable, then the following will be shown:

bash: warning: x: ignoring function definition attempt
bash: error importing function definition for `x'
hello

If you are vulnerable, then you will see:

vulnerable
hello