I was disconnected from Runescape and tried logging on again, but it said I was already on and to wait 60 seconds. So I waited 60 seconds and I tried again, but it still said the same thing. I restarted my computer to see if that would help, but it didn't. Does this mean I'm being hacked or is it just a problem with Jagex?

ive had this happen to me just wait a bit itl come back on i was hoppin for essence in shilo and i had the same thing dont panic for 1 hour it did the same thing but soon jagex will log you out

ok thanks I was able to log on after like 5 minutes of waiting

The reason why is that the alanta servers went down (don't know about others). Since they did, they "lock" your account if you were logged in while they crashed.