Honestly, whoever has an idea for a spam detection measure for Mastodon, and by that I do mean an implementation, get in touch with me, I'll pay for it.

I've been thinking about solutions for the past few days but the more I think about them the more they appear pointless.

Defining an account as suspicious when it has no local followers can be circumvented by just pre-following them, using account age can be circumvented with sleeper accounts, blacklisting URLs does nothing when the spam does not include URLs, checking for duplicate messages sent to different recipients can be circumvented by randomizing parts of the message...

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E-mail deals with spam using Bayesian filters or machine learning. The more training data there is, the more accurate the results, a monolith like GMail benefits from this greatly. Mastodon's decentralization means everyone has separate training data, and starts from scratch, which means high inaccuracy. It also means someone spamming a username could potentially lead to any mention of that username be considered spam due to the low overall volume of data, unless you strip usernames

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However, if you strip usernames from the checked text, the spammer could write messages using usernames...

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@Gargron do what WTDWTF does

there's no secret magic to it

users require a published post to edit their profile
users with zero or negative upvotes require mod approval to post
registering an account from an IP that is already associated with an account requires admin approval

about a month into this policy the spammers completely gave up

@ben We don't have a true emergency with spammers signing-up on a given instance. Approval-only registrations mode is a good tool for weeding those out. The problem we are experiencing is the spammer signing up on random open instances and sending spam remotely. Therefore, solutions based on IPs or captchas are not appropriate. Even if we release the perfect protection against local spammers, servers that haven't upgraded will continue to make this a problem.

@Gargron @ben We need to stop thinking about handling spam going out and start thinking about spam coming in, then. My instinct here is to read individual posts on their way in and handle spam detection at that level (likely on a separate lower-priority thread/task/whatever to prevent lagging out incoming posts).

@bclindner @Gargron @ben That imposes the cost on the victim of spam, which leads to an arms race. Better to try to impose the cost on the spammer.
Perhaps allow an instance to enable a setting that says if sending instance is n versions behind, reject messages?
Zombie instances would get gradually de-federated.

@daedalus That might help as an intermediate step but currently our problem exists with no real spam filtering existing on the Mastodon system whatsoever save for some rate limiting.

I'm honestly glad nobody's set up an auto-spammer script. We might be well and truly fucked if that happens before we can implement proper spam detection systems.

@Gargron I think one important aspect that has been pointed out by @ben is that users can be asked to classify the people they follow, and this can be used to compute some kind of credibility score for the new profiles, in order to limit their activity on a timescale at which modération is effective. I don't see any automated solution, tbh.

@gargron @ben if an instance has open registration and refuses to update their service to deal with spam, I don't think it's unfair to defederate with them.

admins are responsible for the servers they run, and if those servers are the source of a disproportionate amount of spam, it doesn't matter whether the root cause is malice or simply inactivity from the admins. the end result is the same.

@ben @Gargron I hate reputation systems, you will just disgust new users if you do that.

@darckcrystale @Gargron we have never had a user with negative net reputation who was not banned for spamming

@gargron Surely a message containing tons of usernames and nothing else would be spam 99% of the time, though, so that doesn't sound like a problem for a Bayesian model.

@Gargron Honestly I'd pay to see someone do that, and then promptly ban them for it 😂

The more I think about email-like detection systems, the more I think as long as implementation is sound, it will help a lot with curbing common spam as the network grows and older instances and instances lots of users amass bigger datasets and higher confidence levels on spam detection.

Imperfect? Yeah. An arms race? Yeah. But it's a start.

@Gargron I can only assume this must be how the early adopters of email must have felt when the system started getting big.

@gargron would it be possible to provide some kind of built in trainable spam detector for Mastodon, and have an opt-in option to share data with a global pool of training data? that way instances could collaborate to fight spam

@Gargron I'm going to hazard a guess that > 90% of spammers aren't going to try to be clever.

An idea for spam containing links 

@Gargron when I was working on online advertising, some of the ads we had in our inventory came from other big platforms, like Tubemogul. To know which brand to invoice for the ad display, we used the clickthrough (the url where the user is sent on click on the ad) to determine the domain of the url, after all the redirections.

You can use a similar system to list which domains are often shared in toot and blacklist them if the number of toot containing it is increasing at a specific time. Then, instance admins would receive a notification and could whitelist them if they want / if it's not spam.

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