http://www.itpro.co.uk/633673/linkedin-cookies-compromise-user-accounts
http://www.pcpro.co.uk/news/security/367540/cookie-flaw-leaves-linkedin-accounts-vulnerable
The problem is that the LinkedIn cookies have an extended expiry time, meaning a bigger window of opportunity for cybercriminals to access these cookies, and in turn, sensitive account information.
Worse still, the cookies remain active even after the user has logged out of their LinkedIn session.
As Narang explained, "In just 15 minutes, I was successfully able to access multiple active accounts that belong to individuals from different global locations. They would have logged in/logged out many times in these months, but the cookie was still valid. Even though you change the password and all settings, still the old cookie is valid and will grant the attacker access to your account." (Source: itpro.co.uk)
http://www.v3.co.uk/v3-uk/news/2072991/linkedin-hit-cookie-vulnerability-claims
http://www.pcpro.co.uk/realworld/365947/how-to-stay-safe-against-session-hijacking