Graphics processors are optimized for performing certain types of calculations. I didn't catch how many of the cards are required for this 2hr timeframe. They are likely using many PC's with multiple cards per pc, not something the average joe will have at home. Maybe in 5yrs from now...
That said, any website with modern security would limit how many guesses can be made in a given amount of time. Typically after the first 2-3 misses they build in a significant delay.
So, This isn't really a web security issue, it's more of a business / enterprise security risk for others having access to local data ie, I put something important on a flash drive and encrypt it with 8 characters and then that gets lost/stolen--now that data isn't so safe.
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