It looks like someone stole from several wallets, mine was just one of that.
Your address was emptied after 3 months, some of the other addresses after
a year or
almost 2 years.
If someone somehow compromised your paper wallet from outside your office, that means they've patiently been waiting for people to make multiple deposits to those paper wallets before robbing them. That may also mean it will happen to more people.
Could this indicate something larger, that Bitaddress itself could be compromised?
I mean, that's exactly what happened to BitcoinPaperWallet several years ago.
(of course, if you downloaded the webpage, inspected the Javascript, and opened the offline page before generating private keys, you shouldn't be at risk of theft).