Interesting information what with Apple users saying that their computers are virus / malware free with this discovery you have to be careful whatever os your using... Feel for you 100btc is a lot to go missing 
All I can say is there is no issue with the security of primedice, I'm hoping OP will consider editing his post within the next few days with the full story of what happened. I'm not going to share what happened without permission but once he explains you will understand why I've chosen not to.
There are users who choose to store hundreds of coins on their account at one time and have had zero issues, if you have any fear just enable 2FA and as long as your PC is secure you should be good.