Question: [This Super User question](https://superuser.com/q/1096317/479461) made me ask, is it really a good idea to keep files in quarantine, when you don't know what they are yet? For what I know there are more or less 2 steps that need to be performed for "losing control" of your system. First there has to be some malicious code to be injected to the system and then there needs to be a way to execute it. So what measures does AV software take for "in quarantine"-files to avoid this? I'm assuming, the case where the user is just executing the file isn't the problem. I.e. how to make sure that not a bug is causing some overflow resulting in execution of the code?

In other words: What does AV software do to prevent execution of quarantined files, and can I rely on them not being able to get executed anyway?

**NOTE:** I'm not asking about the ways AV's are performing the quarantine feature. The core of the post is: "What are the ways quarantine features are protecting themselves/quarantined files from beeing tricked/decoded/whatever and getting executed anyways and how likely is it this could happen?"

Answer: 
The quarantine AV features mentioned in the reply before make sure that the file cannot be executed or accessed while under quarantine. So no, as long as the antivirus is working, there is no danger for the virus to escape quarantine. Practically, some store the file in a different non-runnable format and some just rename the file and deny read/write.execution access to them.

A simple example: you get a standard file with ASCII .exe content, convert that content to binary and re-write it as zeros and 1s into a text file. Nothing can go wrong from there. There's nothing to escape since the file is now binary content saved as text.

-Edit-

So the elements you asked about are Deny R/W/X access and encode the file into anything else but the original format.
Suppose you have an important file(say, some presentation) that is flagged by your antivirus as "malicious". You do not wish to delete it(it's important after all, even if it is malicious!), but you don't want your machine to get infected as well.

So, what option do you have? Your antivirus product can `quarantine` it. It keeps the files in an isolated environment on your disk, so that malicious files do not pose a threat to your machine.

There are different approaches as to how these files can be handled:
1) moving the file to a different location
2) renaming the file, changing the format of the file
3) changing the permissions of the file, marking it as hidden
4) encrypting or encoding the file, so that even accessing the file would render the malicious code useless

Now what if you want the file back, even after you understand that it might wreak havoc, or might be just a false-positive? Antivirus products give you the option to move the quarantined file from quarantine to the original location, in the original format, so it is usable again for you(at your own risk, of course!).

If you strongly suspect that your file is harmless, you can try scanning it with other antivirus(say, on [Virustotal](http://virustotal.com)). You can also ask your antivirus product vendor to recheck the file for any malicious behavior. Once you're satisfied that it is harmless, you can safely go ahead and restore the file from quarantine.

And yes, you can rely on quarantine features of any reputed antivirus product.