No, I neither downloaded any file except the DOGE-Coin wallet nor opened anything in skype. It seems very strange to me too ...
Strange indeed. Legit OS copy or a pirated version? Those might have trojans, backdoors as well. You dont need to answer this, just consider it an option. Other possibilites I can think of are:
#1 infected machine in your LAN that used an undocumented exploit on your the unpatched OS (infected after/durring setup).
#2 infected infrastructure (e.g. your router) - this would also need some sort of vulnerability of your OS or local file sharing
#3 data leak (e.g. shared the data via dropbox with your colleges)
#4 someone had hardware access to your machine (made the TX from there/copied the wallet.dat/installed something)
#5 drive by infection
#6 you use(d) WinXP or older
The OS is a legit copy, but after a complete scan of the system the antivir found three threats:
#1 "Virus found: Win32/Zperm, C:\Windows\Temp\49f48af4-b402-4745-9e9c-26cfb8983c1f\tmp0000116d\tmp00006408";"Saved"
#2 "Trojan: PSW.OnlineGames4.ZUJ, D:\buddha.dll";"Saved"
#3 "Trojan: CoinMiner.ASJ, C:\Users\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.IE5\ZLLU0VPX\wmpnetwk[1].dll";"Saved"
I think we found the colprits, but again, it seems very strange to me how they could infect the system. Inever opened any suspicious software nor I am using IE as my browser. I am on Win7 using a brand new Cisco X3500 router and it is the only cmputer in my appartment, but I have learned my lesson: be paranoid as possible, but I doubt that BTC ever arrive to the "normal" users since it is that easy to get stolen and it is to complicated to be on a save side, e.g., using linux, live cds etc.