OK, no attack this time, but it could have been some evil page with a java script on it that did anything to your machine.
If so, then sorry it's too late now, by clicking on the [Sandbox] link you just invited in a TrojanHorse? to do whatever it liked.
Possible responses to the risk
- when you see a [link] take the [ ] as a reminder to look at the url (many browsers display it at the foot of the window) before clicking on it. UseModWiki never fakes the url displayed there - because you never know when someone sneaked in to edit the page, you don't just look the first time you access the page, you look every time, like you look every time before crossing the road
- don't use [Foo] links at all
- (if you own a wiki) set the config to disable this feature
- who cares? - wiki is about cooperation and mutual trust. I'd rather have it pretty and trust my fellow wikizens