That happened to me exactly the same way, back in December. Finally, traced it to Bittrex. Lessons learned: Hacking an individual's machine is easier than hacking a bank. Top security practices are needed, else, keep your money in the bank.
Yes lesson learned.
I found out that POS coins like ARCH are a greater security risk if you are staking them as you make yourself a target for people prepared to hack as anyone with a wallet can see your on the network 24/7
No one attacked the ARCH network and it is not a security risk to stake your coins. Leaving any unencrypted wallet file on your computer is idiotic, if you lost your coins it is your own fault.
I have been staking my coins for over 6 months and my balance only goes up. Do you know why? My wallet is encrypted.
What is the relevance of those wallets that you linked? If they have 32,000 coins they can probably access CEO info.
Encrypted wallet, VPN, sandbox, don't use TeamViewer or other cloud services on your staking machine. Common sense, done.