blog about spam filter

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+---
+author: edk
+date: 2018-09-24 17:47:00+00:00
+slug: spamfilter
+title: Spam filtering
+category: freenode
+category: announcements
+---
+
+Hi,
+
+As most of you are aware, we've been experiencing significant spam over the
+past few weeks. As a result, we have decided to roll out a server-side spam
+filter. Unlike our current spam-mitigating techniques, this system applies to
+private messages and does not let the first matching line get through.
+
+Various ethical concerns have been raised over the course of introducing this
+feature. They'll be addressed below. The short version, though, is that the
+system has various limitations built in designed to prevent operator abuse.
+Only a tiny bit of information can get out of the filters, and they do not have
+access to much information themselves, to the extent that we believe the
+obvious ways to abuse such a feature are impractical.
+
+We've historically been reluctant to take steps like this, and we remain so,
+but we believe the disruption has reached such a level that this is necessary
+to allow the communities using freenode to collaborate effectively. The
+current complement of anti-spam measures represents our preferred approach,
+and we intend to employ this only when, as in this case, they prove
+insufficient to minimize disruption.
+
+
+- _Could this be used to spy on users?_ Which filter a user matched is not
+  reported to staff, only that one did. This limits the theoretical maximum
+  rate of passive monitoring to one bit per message, far less than the
+  information content of conversations.
+
+  Recipients of private messages are not included in the line that filters
+  match on, so staff cannot use spam filters to see who is talking to whom.
+
+- _Could this be used to shadowban users?_ No. If a filter blocks a message,
+  its sender is either disconnected from the network or sent an error message.
+
+  Currently, the filter system is configured not to use the nick, username, or
+  hostname for filter matching, so it can't discriminate against particular
+  users at all.
+
+
+The exact information filters "see" is as follows:
+
+- The type of message (PRIVMSG/NOTICE)
+- The target of the message, if that target is a channel. For private
+  messages, filters can see that they are PMs but not who their target is.
+- Whether or not the sender is identified (but not their account name)
+- The full contents of the message
+
+The code can be configured to filter on the `nick!user@host` of the sender. We
+haven't enabled this, and have no current plans to, but this is subject to
+change should the nature of the spam demand it.
+
+Filtering is always performed on the server originating a message, and inside
+the ircd process. This system will never cause a message to be distributed
+more widely than before.
+
+Staff can, as always, answer your questions about this change, and we welcome
+constructive feedback. Private messages to staff are not subject to filtering.