"Open Groups" on LinkedIn, lets anyone view all discussions on the web, found on any search engines, and can be shared on other social networking platforms like Twitter, in addition to LinkedIn.
"Whether or not to make a group open is entirely up to the group's owner. If he or she switches to an Open Group, we'll immediately let all members know about the change and future discussions will be viewable online. Past discussions will only be accessible to group members, through a members-only archive," explains LinkdeIn
Any LinkedIn member can now discover and follow specific discussions of interest in any open group, even without being a member of the group.
In many cases, you can join right in. But the powerful, flexible moderation tools that we recently rolled out for maintaining quality conversations in groups will allow managers of open groups to specify who can contribute and how.