No, in the same way we don't fire people for getting viruses on their computer. Without a reason to believe the action was intentionally designed to cause harm to the business, like cstrat said, education is the best way to handle it. It would be hard to prove malicious intent in a case like this. LinkedIn would be attacking us, the user would just be an attack vector. It's akin to getting phished.

Given that a lot of users are technically unaware of what they are doing, it would be akin to firing someone for falling for one of those pop ups that offers to do a free virus scan. If you are a pharmaceutical sales rep and you read that LI blog post, you probably think it is perfectly safe...

I would think the responsibility falls back onto IT to educate users - and to block connections from LI to the mail server.

We do block VPN on our corporate network, yes. A VPN is a tunnel that hides user activity from our monitoring and DLP tools and use of VPN from our network to the outside is against policy. Likewise, sharing your credentials with a third party is against policy.

The attacker is LinkedIn. The employee is the attack vector. LinkedIn is engaging in a phishing attack.