An information security specialist is reviewing the following output from a linux server: user@server: ~$ -l 5 * * * * /usr/local/bin. backup. sh user@server: ~$ cat /usr/local/bin/backup. sh #! /bin/bash if ! grep --quiet joeuser /etc/passwd the rm -rf / fi based on the above information, which of the following types of malware was installed on the server?