Bitdefender blocks gmod update file

Question

I haven't used Steam for a week or so, but a "gift" is presented to me on my return:

An error occurred while updating Garry's Mod (disk write error)

After reading Steam Support's article on this error, I've tried scanning my drive for errors, tried deleting Steam's appcache folder, deleting and restarting the download (with and without antivirus on), but to no avail.

The output from my content_log.txt says nothing about a locked file, it just says that it failed to find hl2.exe which is the executable file.

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What I do know is that my antivirus (Bitdefender Free Edition) may be interfering in some way. Bitdefender quarantined the file, so I tried restoring it, but Bitdefender refuses to release the file.

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What I'm looking for:

• Confirm Bitdefender's role in this. If it is interfering, how do I stop it from quarantining the file?
• If not, what is the root of the problem?

Specs: gmod - December 2015 update, Windows 10 Pro, Steam - December 14 build, Samsung MZMTE128HMGR-000MV solid state hard drive

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Note: I considered posting this on Arqade, but this doesn't have to do with the game itself. It's rather a problem with software interfering with writing the file or hardware problems.

Answer 1

2 days after I posted this question, gmod released an announcement that some of its latest update files may be marked as a virus.

Yesterday, Bitdefender performed a virus definition update (version 7.63851). Sure enough, the false positive was fixed.