The vxCrypter Ransomware could be the first ransomware infection that not only encrypts a victim’s data, but also tidy’s up their computer by deleting duplicate files. It is not known why the ransomware is doing this other than as a possible way to increase the speed of encrypting a computer. It also illustrates how we have to stay alert as attackers continue to evolve malware to increase performance, cause havok, or just do things for no obvious reason. The ransomware is only deletes duplicate files for the following file extensions that it targets for encryption.
Source: https://www.bleepingcomputer.com/news/security/vxcrypter-is-the-first-ransomware-to-delete-duplicate-files/