You must enter a password to access the install-tool. The password is set in localconf.php:

$TYPO3_CONF_VARS["BE"]["installToolPassword"] = "bacb98acf97e0b6112b1d1b650b84971";

If you insert this line in localconf.php, the password to the Install Tool is 'joh316'. Changing the password can be done from inside the tool.

$TYPO3_CONF_VARS["BE"]["installToolPassword"] = "";

Setting the install tool password to empty (default) the tool will exit immediately with the message “Install Tool deactivated”.

Please read the security warning in the Install Tool and take proper action. If you're in doubt, simply remove the script typo3/install/index.php