For more information on Spamming, read the Spam article.
What is a Spam Bot?
How to Detect Spam Bots
You can usually tell if you're looking at a bot message if it contains a bunch of nonsensical jargon, or if it contains out of scratch links.
Where are Bot Messages mostly found?
Most often the programmers who make the bot will choose to spam the more active forums on Scratch, such as the Show and Tell, or the New Scratcher forums, as the spam post will be seen by more people. Spam Bots will also sometimes attack in the form of comments, whether on profiles or projects.
How to Deal with Bots
Don't reply to the messages. Simply report them. If you reply, you're really just making more work for the Scratch Team since they now have to take care of both the spam message, and your reply.
How does the Scratch Team deal with the bots?
They will ban the account that made the post, as well as possibly administer IP bans etcetera to ensure that no other bots can be made from that point. They will also delete all offensive material that the bot made.