Using free software to protect your computer is like hiring a music major to run your IT security.
Not to mention, you don't need CCleaner or similar software anymore. It's much more likely to cause a problem than fix it. Some people swear by it religiously, but I've literally never seen a case where it was particularly useful on a recent OS.
Maybe we're thinking different scales here, but we use a LOT of free (as in beer and speech) software in enterprise security operations on a global scale.
Chris
I don't think he's referring to serious FOSS like ssh, nagios, OpenVAS, nmap, snort, etc. He was probably meaning crap grade ad delivery software that pretends to be useful. Plenty of that around.