If you have a LinkedIn account, you should change your password today.
Out of the approximately 150 million LinkedIn accounts, 6.5 million (5%) of them had their passwords, in an encrypted form, stolen on Monday. The hackers are now in the process of cracking that encryption and that is expected to take only a few days.
Linkedin is apparently investigating and has not made a formal announcement but the hack has been confirmed by several notables and the data is available on hacking websites.
Also note that if you are using LinkedIn from an Apple or Android product, some of your personal information was being sent to LinkedIn without your knowledge or approval. Yesterday, the LinkedIn Apple and Android apps were updated to not transmit this information so if you see an update to those apps, you should consider installing it.