First of all, reviewers only have access to the online forum for their own submissions and only when you activate this functionality.
You can change the settings for reviewers to be able to discuss their reviews in the online forum or have access to co-reviewers’ reviews here:
Overview => Settings => Main Settings for the Review Process
In the section “Access to Reviews of Co-Reviewers? / Access of Reviewers to Online Forum?” you have a number of options for reviewers. You can choose between general access to co-reviews of the same submission, access to co-reviews only after having entered a review and access to co-reviews and online forum after review submission. For all three options you can choose between anonymous and non-anonymous settings (see image 1).
Furthermore, you can change the settings for anonymity for messages sent via the online forum in the section “Show Names of Message Authors” (see image 1).
By default, reviewers do not have access to the forum. If you give them access, reviewer names are, by default, not shown.
If you give PC members access to the forum in Phases and Deadlines, they have access to reviewer and PC member names.
Please note that you can also define if the names of the authors are shown in the forum.
By default authors’ names are not displayed. The setting can be changed for each individual submission type / track.
Overview => Settings => Manage Submission Types / Conference Tracks
Select the corresponding track, select the edit button and on the next page scroll down to the section "Review Options".
If you enable the setting "No, single-blind reviews" for the option "Double Blind Reviews", the names of the authors will be displayed in the online forum to the PC members (see image 2).
Chairs, on the other hand, can always see the names of the authors and the reviewers in the online forum. This setting cannot be changed.