OpenStreetMap has a series of mechanisms to combat malicious editors. Mostly they get found out quickly by local mappers and problem edits are reverted. Sometimes it takes a while, but it happens. Also, with lots of editors, sometimes the problems just get fixed as data is changed.
Some power users monitor the map closely, and OSM does have a (very small) number of moderators who can block malicious users.
OSM is also working on actively improving communication about edits, so problem users can be identified more quickly and efficiently.
Source: I'm the author of that blog post, I'm also one of the aforementioned moderators, and I'm also working on the improved communication (it's OSM's GSoC project this year).