Downvote and comment. Starting the comment with the word Danger! in bold ought to be fairly obvious, especially if the answer is sitting at a score of -1.

That said, I've never seen an answer be intentionally malicious. If a user has a pattern of doing that, a custom moderator flag would be in order. You shouldn't otherwise flag a wrong answer; votes are what rate helpfulness.

Downvote and comment. Starting the comment with the word Danger! in bold ought to be fairly obvious, especially if the answer is sitting at a score of -1.

That said, I've never seen an answer be intentionally malicious. If a user has a pattern of doing that, a custom moderator flag would be in order. Otherwise, a flag on a clearly malicious answer may or may not be marked helpful.