Here is a quick way to find your old WP installs that might be open to cyber attacks.
Code:
grep 'wp_version =' */wp-includes/version.php|grep -v '3.5.1'
Each time the version changes just put the correct one in the end of the command line code.
Also, you might have to add something to the */wp-includes like */htdocs/wp-includes or */public_html/wp-includes to make up for how your server is handling where your installations are compared to your user directory.