I'm still a relative noob, but I've just had my first encounter with a spambot flooding multiple posts with a short message of support: "Simply Great Information and Presentation". However, despite seemingly liking the content, the user does not upvote the post.
At first I thought this is annoying, but no harm done. But then I looked at the user's other posting activity and saw that quite a few post authors upvoted the comment, giving the spam author rewards. I've flagged some, but I'm just a minnow, so calling on support from those with more steem power.
Also, my post https://steemit.com/census/@brendio/australian-census-online-fail recieved the comment twice, so it seems the bot has a bug.