I logged in to Splinterlands this morning to find that all my DEC and almost all of my cards were gone. It wasn't much in the grand scheme of things - 500 DEC and about 25$ worth of cards, but it was a lot to me and even if you ignore the monetary value it's still an invasion of my privacy which has soured me on humanity a bit.
My faith in humanity was somewhat restored when I asked the nice people on the Splinterlands discord for help with this and got both sympathy and concrete help with what to do.
Tracking down the guilty party
Of the advice I got, the first one I acted upon was to track down who stole my assets using hiveblocks.com. When I looked up my accounts transaction history, I found I had apparently gifted a lot of cards to a user called 
I looked up his market history on Peakmonsters and wow - there was a lot of transactions. Some of the cards I recognized as cards I had lost, so some of them were probably mine.
His history of card sales went on for several pages and that was just for October 19th.
Consider this my official warning for this guy. He's up to no good and I recommend everyone to now deal with him if you should end up in contact with him somehow.
Next steps
I sent an email to the splinterlands support and opened a ticket to see if there was anything they could do to help. From what I've heard, there isn't much they can/will do about things like this, but I told them that
If anyone from the devteam reads this post: Even if I can't get my assets back, this kind of theft can't be allowed to go on and I would at least like to see some kind of action to increase account security be taken so that this will be harder to pull off in the future.
Increasing account security
I don't know how this guy got my account details, but the most likely reason is that my email was hacked. To combat this, I changed my passwords and activated Two-factor authentication. I then changed all my hiveaccount keys and stored them in a more secure location than I had previously in case those had been compromised.
I use 2FA quite a lot and the fact that I hadn't activated it on my email is a mystery to me and a mistake I now seem to have payed for. I recommed all of you who read this post activate it everywhere you can. It really helps.
I don't know if I had accidentaly logged onto some shady site with my HIVE-account. I don't think I have, but I will be extra careful in the future of where I use the keys anyway.
Future
Unfortunately I can't really reinvest what I lost in this hack into the game at this time, so I will probably take a little break from Splinterlands until I can get back into it for real. I really like the game and I hope to see you all around in the future, hopefully with a much more secure account!
/Dirtyharry94