It’s highly recommended that all users upgrade to 1.6.9 to patch the security issue. Details of the vulnerability will be published after users have had time to upgrade. In addition to patching the security issue, this version also improves the debug log by hiding data such as the ABSPATH directory of the WordPress install and login cookies.
“Unfortunately in the past users have copied the log file data into forum posts. A warning message has been added asking the site owner not to publish the debug log,” Donncha Ó Caoimh said.
Also worth noting is that after updating to 1.6.9, existing debug logs will be deleted.