Re: New electrum version detected as Trojan by Bitdefender
I was on 3.3.4 and was trying to upgrade to 3.3.6 which showed up on my wallet
The above comments have given enough answers with a lot of details but how can this happen? 
Did you download the antivirus software (Bitdefender) after downloading the old wallet version "3.3.4"? If this program is already installed you will get the same error in previous versions.Check the signature and follow the official twitter account to check for future problems.
it sometimes is because of the changes they make in the application and add or remove certain functionalities and sometimes it is because those changes are creating certain hashes in the signature of the files that resemble a virus signature which then is caught as "suspicious" by the antivirus program.
the other possibility is the upgrades in the AntiVirus itself which adds new virus signatures so it starts detecting these things as Trojan,...