A hacker in Russia claims to have stolen login details of 6,458,020 users of the popular business networking and job searching network.

Social networking site Mashable has recommended that users change their passwords immediately.

Chief Research Officer of internet security firm F-Secure Mikko Hypponen told The Verge that he considered the password leak found on a web forum was “a real collection…it’s some sort of exploit on their web interface, but there’s no way to know. I am sure sure LinkedIn will fill us in sooner or later.”

The hacker who claims to have stolen the database has been requesting help online from the hacking community to deal with the site’s encryptions. 

The level of security on LinkedIn has been criticised by some users for not using ‘salted’ cryptology which can prevent password hackers from using a ‘dictionary attack’ – which involved using an automatic search using existing words found in a dictionary to guess passwords.

Main photo: Linkedin founder Reid Garrett Hoffman and CEO Jeff Weiner (Getty images)