If I am not wrong, to be able to send mails through SMTP, first you need to verify your self with user id and password. Thats why this hack needs ur logins to connect. "Nobody" is simply using php mail function to send mail.. so I don't think your SMTP is insecure.
I think you could edit the settings if u still fear in SMTP conf file.
I could not get it to work

. I haven't tried the second attachment which Illuvator gave. I tried it, but did not work.. so i am trying what Zach gave.
Getting this error:
Fatal error: Call to undefined function: errormessage() in /home/torrents/public_html/includes/mail.php on line 235
at Line 235:
if (!$this->sendMessage(".", 250))
{
return errorMessage("Unexpected response from SMTP server");
I got that code. However, I disabled SMTP tweak, also checked my server doesnt allow to send mails as "NoBody".
EDIT:
I could send mail to single user through diagnose tools, but when I send mass mails I am getting this error:
Fatal error: Call to undefined function: errormessage() in /home/torrents/public_html/includes/mail.php on line 218
The line I got in mail.php at 213 - 219 are:
if (!$this->sendMessage(base64_encode($this->smtpUser), 334) OR !$this->sendMessage(base64_encode($this->smtpPass), 235))
{
return errorMessage("Authorization to the SMTP server failed");
}
It can't be wrong password, because it is able to send mail to a single user. It sent to one person in mass mail list, it only occured for second > user.
Any idea how to overcome it?