It's probably safe to assume that most computers are running
some sort of insecure application. That's not always the fault
of the administrator (in a business) or the end user (at home).
After all, if an existing vulnerability hasn't been discovered
or made public yet, then we certainly can't work to mitigate the
problem. On the other hand, if administrators and end users of
PCs aren't checking for known vulnerabilities and the
availability of updated versions of their software, then
responsibility for related insecurities resides firmly with
them.  According to data gathered by Secunia (available at the
URL below), approximately 95 percent of all computers have one
or more insecure applications installed such that remedies to
those insecurities exist but have not been integrated. The
bottom line is that most people are not patching or upgrading
their software when security updates become available.  Secunia
gathered the data using its free Personal Software Inspector
(PSI) tool, which is available for Windo