If you want to restrict access for a user to several containers from different Projects, you can create a new security group with the Standard Viewer template and then create a Dynamic Virtual Container with the items in it that you want the user to have access to.

1. Create a new security group with the Standard Viewer template.
2. Right-click on the Project, go to Configure > Permissions > Configure and select the new security group.
3. Unselect Allow for all permissions except View Content.
   Note: Do not select Deny for these permissions; only unselect Allow.
4. Create a new Dynamic Virtual Container and select the items from the different containers that you want the user to have access to.
5. Select Direct Access while creating the Dynamic Virtual Container.
6. Right-click on the new Dynamic Virtual Container and go to Configure > Permissions > Configure and select the new security group.
7. Unselect Allow for all permissions except View Item.
   Note: Do not select Deny for these permissions; only unselect Allow.