Older versions of BDLib for Minecraft 1.7 – 1.12 contain a known security vulnerability.
You can read more about the vulnerability here – https://blog.mmpa.info/posts/bleeding-pipe
I’m releasing updated builds for 1.7.10 and 1.10.2,
a version for 1.12 will be available soon(tm).
Updated: A version for 1.12.2 was added as well.
In general I do not recommend playing those old versions on public open servers, even with those fixed versions – there’s still many other known vulnerable mods from other authors out there.
This does not affect single player.
If you do want to play multiplayer I recommend installing one of those 2 mods, though I can’t guarantee they completely fix the issue – https://github.com/dogboy21/serializationisbad/releases or https://modrinth.com/mod/pipeblocker