Cyber- Attack - What is Petya ransomware?

What is Petya ransomware? 

A variant of the Petya ransomware, which has been around for more than a year, was blamed for Tuesday's global attack. Petya is a vicious form of the virus that locks a computer's hard drive as well as individual files stored on it. It is harder to recover information from computers affected by this ransomware, which can also be used to steal sensitive information.

Cyber security experts Kaspersky Lab released a conflicting report that said the ransomware was not related to Petya but was in fact a new program it called NotPetya.   

How does it differ from WannaCry?

Security experts said the program could have spread in a similar way to the WannaCry attack that hit hundreds of thousands of computers including the NHS earlier this year.

Like WannaCry, Petya could have used Eternal Blue, a tool created by the National Security Agency and leaked online by the Shadow Brokers that exploits a problem in Microsoft's software.