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Without knowing root cause this problem can arise again. How did it happen? Is there an antivirus installed? Is it updated regularly? If yes, then how did it possible? What OS is there? Assuming this is Windows, is it updated with latest updates?
There are several ways to overcome this issue, but you have to know the root cause for your future security.
There are some free solutions like you can try with SpyHunter that can help to over come this issue. Also here is a good link, https://www.avast.com/c-ransomware