[ikesau]

There's arbitrary "accuracy lowering" vandalism done by (i suspect) bots that alters dates by a few days/months/years, changes the middle initial of someone, or randomizes the output in an example demonstrating how a cipher works.

it can be hard to spot if no one's watching the article. puts me in a funk whenever I catch it.

[marcosdumay]

Some people edit chemistry articles replacing the reactions by stuff that doesn't make any sense or can't possibly work. Some people changes the descriptions of CS algorithms removing pre-conditions, random steps, or adding a wrong intermediate state. And, maybe the worst, somebody vandalizes all the math articles changing the explanations into abstract nonsense that nobody that doesn't already know their meaning can ever understand.