The script author was trying to spawn a local shell by using the os.system() function, which executes a command in a subshell. The command being executed is "/bin/bash", which is the path to the bash shell, a common shell program on Linux systems. The script author may have wanted to spawn a local shell to gain more control or access over the compromised system, or to execute other commands that are not possible in the original shell. The other options are not plausible explanations for what the script author was trying to do.