Just because the anti-virus deems the file a virus it doesn't mean it is a virus. It just means the file is using processes, commands, or contains code that the anti-virus does not want programs to use. In d2loader's case this is a legitimate use but anti-virus doesn't distinguish between bad or good uses.
Norton is especially sensitive when using loader. It's actually quite funny because my Norton gets all pissed off when d2loader file is placed in my DiabloII folder but I have the same file in 3 different places on my harddrive and Norton does nothing to remove or warn me of those.
Still can't get Norton to ignore the file so I put a d2loader folder in my DiabloII folder so I can let Norton do its' removal and stop bothering me and I just copy the file from the folder and put it back whenever I'm ready to play again.