There was a questionable post caught by SmokeDetector containing an invisible link set forth on white space like follows:
[ ](hxxp://some-nsfw-image-link-or-spam-link)
... which renders pretty much as a 'space', as is the example here between these parentheses (note that in this case, the invisible link i put in there goes to https://meta.stackexchange.com, so people don't think I'm spamming or anything): ( )
This is definitely an evil vector, and makes for 'invisible' links which are hard to find unless you're looking at markdown or SmokeDetector's detections on it.
I believe that, if possible, such markdown replacement of links that use white-space-only in the square brackets should be automatically "removed" by the post system. This removes a hard-to-see 'spam linking' vector that might otherwise only be caught by SmokeDetector.