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.
Hi, OP here.
Stunna has been incredibly helpful in the situation so far. The current theory is that a thief must have compromised my account by brute-forcing my weak password. Since there would be no way for anyone on the outside to know exactly when I had been online at PD (since I did not make any bets or make my presence known in the chatroom on the day of the theft), they must have been monitoring the blockchain for large deposits from my personal wallet to my PD address somehow. Possibly through the use of some script? I have no clue...
I have to hand it to the thief for having enough technical know-how and impeccable timing to pull off the withdrawal in the incredibly small (literally 2 minute) window between confirmation and my first attempted bet.
If anyone out there has seen this type of theft before, PLEASE LET US KNOW any details you have, as this is the first time I have seen anything like it.
Now that 2FA is available, hopefully this will be the last time.
Thanks,
DiceMiner
Got to hand it to you Diceminer, you have handled the situation with the utmost respect. With that type of money on the line, I think I would have been running around screaming. You obviously are a very level headed individual. Sorry you lost so much coin, I hope that we all have learned a valuable lesson here. Always use 2Fa and use very long difficult passwords. Also, it may be wise to only put on the site that you are wiling to lose, i guess you did this, because you are gambling, lol.
Kudos to you and Stunna..