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Decrypted files are safe?


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#1 keysteal

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Posted 08 December 2016 - 08:16 AM

I had yesterday a conversation with a new customer that was infected by a ransomware, and they already paid the ransom and today they've received the decrypter program. My question is: decrypted files are considered safe next? What tools can I use to scan the computer that started the encryption and be sure that will be safe after? (p.s. could it be useful to use a rescueCD?)
p.s.: i asked to this customer to copy an encrypted file and the decrypted, to give them to this community to be studied. I will go to them tomorrow hoping to be useful to going back to work safely.
Thanks in advance.

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#2 quietman7

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Posted 08 December 2016 - 05:35 PM

Most crypto malware ransomware is typically programmed to automatically remove itself...the malicious files responsible for the infection...after the encrypting is done since they are no longer needed. The encrypted files do not contain malicious code so they are safe. Unfortunately, most victims do not realize they have been infected until the ransomware displays the ransom note and the files have already been encrypted. In some cases there may be no ransom note and discovery only occurs at a later time when attempting to open an encrypted file. As such, they don't know how long the malware was on the system before being alerted or if other malware was installed along with the ransomware. If other malware was involved it could still be present so be sure to perform full scans with your anti-virus. Disinfection will not help with decryption of any files affected by the ransomware.

If your antivirus did not detect and remove anything, additional scans should be performed with other security programs like Malwarebytes Anti-Malware, HitmanPro and Emsisoft Anti-Malware. You can also supplement your anti-virus or get a second opinion by performing an Online Virus Scan...ESET is one of the more effective online scanners.


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#3 keysteal

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Posted 10 December 2016 - 07:12 AM

I've got an encrypted and the same decrypted file available to be studied by the community. Where can i upload them?



#4 quietman7

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Posted 10 December 2016 - 07:30 AM

Samples of any encrypted files, ransom notes or suspicious executable's (installer, malicious files, attachments) that you suspect were involved in causing the infection can be submitted here (https://www.bleepingcomputer.com/submit-malware.php?channel=168) with a link to this topic.
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#5 keysteal

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Posted 10 December 2016 - 11:47 AM

Thank you for helping me. Yesterday I used ESET rescue cd  as you suggested, but strangely no virus was found. I instead installed

an Avast Security and after a scanning, it only found a virus inside the decryption software, but no other virus was found.



#6 quietman7

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Posted 10 December 2016 - 01:10 PM

That's good to hear. As I said most crypto malware ransomware is typically programmed to automatically remove itself but its best to check anyway.


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