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Recently my AV has been detecting Trojan backdoors, Rootkits and Worms quite often. Some go unnoticed (I've checked suspicious files in VirusTotal a few times and they indeed turned out to be malware without the AV detecting them).

I've tried cleaning up, but in the end I decided to do a clean Windows reinstall. Since I have no other way to back up my files, I'm uploading them to cloud storage. My question is, is there a chance of the malware attaching itself to these personal files (pictures, videos, notes, etc) and once I download them to the new system to end up infected again?

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Usually a non-executable file can not contain a virus. Only executables can cause damage. But there are two cases where a non-executable document can cause the application which opens it to act as malware:

  • The program you open the file with has an unpatched security vulnerability which can be exploited by a specifically manipulated file to cause the program to do things it is not supposed to be doing. When a good(!) software company gets notified that their software contains such a vulnerability, they will usually update their software to fix the problem ASAP. So this problem can usually be mitigated by making sure that all software you are using is always updated to the latest version.
  • The program you open the file with allows documents to include script-code which allows implementation of virus-like behavior ("macro viruses"). The Visual Basic Scripting in MS Office documents is a prime offender for this. Later versions of MS Office now ask you before executing macros. Do not allow this in files which you got from a suspicious source or from a compromised system.

Also keep in mind that executables on Windows can come with many more file extensions than just .exe. So when you aren't sure what a file extension means, do not double-click the file.

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  • Thank you very much. To make sure I got it - this does apply to non-virus types of malware, right?
    – Nayeri
    May 5, 2017 at 13:41
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    @Nayeri The terms "Malware" and "Virus" are used interchangeably nowadays. But if you want to be pedantic and define "Virus" as "Malware with automatic propagation functionality", and you are sure the malware you are dealing with doesn't have this, then you don't need to take any precautions to avoid reinfection. But can you be sure?
    – Philipp
    May 5, 2017 at 13:45

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