I've got the task to patrol the Sirius Sektor and eliminate 3 threats (dont know the real quest-text)
But the Sirius Sektor is the hole Sektor (where to find Sol-System for example) how can I find threats in there?
I've locatet an "Enemy Contact" or something flying around in this Sector, but everytime I engage them (i'm portet to the instance) the game says "well done, thanks for your help", but I didn't do anything and I dont get any quest-progress (1/3 etc.)
You probably came in at the end of an instance. They take 5 minutes to reset after a round is complete. Just hang out and wait for the next one to start. You can get all 3 patrol credits if you stay there for 3 rounds.
Firstly, I believe it tells you to patrol the entire Sirius Sector Block, which covers all 3 sectors (the entire space in your Area Map).
Secondly, the Patrol missions tell you to go to specific Systems, while the Secure missions have you located Enemy Contacts. And when you do enter an Enemy Contact zone, it might tell you "Good job!" but that's just because the instance ended and you have to wait up to 5 minutes for the instance to reset. Only once it resets are you given credit for enemies killed. If you don't want to wait, try finding another Enemy Contact.