My guess is somebody gave their address book to LinkedIn
Obviously so. Jason also commented:
Just need to be careful letting sites and apps go through your email contacts
Not just "be careful" but more like: "Do Not allow" sites and apps any access to your email contacts at all. Ppls contact info is not owned by whoever has the person in their Contacts list. Maybe a link could be added to the WLUG mailing list signup page, sending a proposed (requesting-to-join) WLUG mailing list member to a page stating Privacy policy (non-share contacts info). If a proposed (requesting) mailing list member must read Privacy policy, then agree (click Yes to Agree) before becoming a member of the mailing list, maybe it would prevent the idea that Contact lists can be so casually given away. Liz J