Thread:Project:Support desk/mediawiki.log.js access denied when backing up (copying) mediawiki folder/reply (7)

"Heur.Dual.Extensions" sounds like it's only a heuristic alarm; the antivirus has not actually found something it knows in the file, it only thinks it might be suspicious. If the file is a true copy of what comes with the MediaWiki package, I think this is a false positive and you should inform your antivirus provider so that they can check and then maybe fix their definitions.