Well, sorry, once the TX is already broadcasted there's nothing anyone can do about it (that's the way it is with all cryptocurrencies, not just Stellite). If the sum is large enough, you might consider contacting local authorities (police etc), but it's very unlikely that they'll be able to help.

Most of the time coins are stolen when the user runs malicious code on the machine that has the wallet file. If that's the case, then you might still have the program/virus/trojan on your computer that is responsible for your coins getting stolen (and it might steal something else from your computer, or even from other computers on your network!). It might be just something you picked up randomly surfing fishy websites. Or it might be some other coin's wallet that was programmed by the devs to fish for other wallets on the computer it's installed on. Or it might be mining software — there's plenty of closed-source miners out there, and some of them might contain malicious code. Finally, if you have some kind of remote control software installed on your computer, this is also how it could be compromised (although less likely).

Then there's physical access possibility — if anyone else had access to your computer then they could make the transactions manually.