Thanks for this howto.
I would suggest some changes, though.
Instead of changing the cron line I would simply add the following below the psa check
elif [ -d "/usr/local/ispconfig" ]; then
/usr/local/maldetect/maldet -b -r /var/www 2 >> /dev/null 2>&1
Before you call the install.sh of the maldet software remove the following line from it:
cp $inspath/inotify/libinotifytools.so.0 /usr/lib/
It should not work anyway copying this file as a symlink with this name exists, but who knows... The line exists 2 times in the script.