You can look at ProcAlert as some kind of firewall. Only this firewall protects your computer from the inside out.

ProcAlert will monitor all running programs on your system, and when a new program opens (even an invisible one), ProcAlert will notify you and ask whether you want to terminate it.

A convenient list with permissions will make it easy to manage all programs that may run on your system. The advanced feature LockDown will even make it possible to prevent ANY program from starting. This is very interesting for preventing virusses to start when you're away, or to prevent unauthorized access to your computer...

Along with this, ProcAlert comes with tons of features, including Password Protection, exporting capabilities, filters, etc...

ProcAlert won't make it impossible for virusses to run on your computer, but it'll defitinely make their life a lot more difficult!

For a more complete overview of the features, I gladly refer to my website.