They are IDs used exclusively for posting in threads, that are never tied to an email address nor your IP, allowing you to post truly anonymously.
No. But using an anonymous ID will lift some restrictions and grant you many privileges overtime, including no longer having to type a Captcha and being able to post through any IP, even a banned one. Click to see all the Anonymous ID Benefits
If you want maximum privacy, it is a good idea to change your ID every now and then. You can do that without having to increase your post count again by donating posts to different IDs. The more different IDs you donate posts to, the harder it is for anyone to know which new ID you migrated to. Check the Post Donation page.
By using anonymous IDs, MasterChan can moderate users without the need of storing your IP on the database. The majority of websites on the internet will store your IP address along with every single post you make. Your IP address is the most sensitive information that you could share online, as that leads to, without a doubt, your physical location. In this age where governments record every connection and hackers can gain access to databases and easily spread their contents across the internet for everyone to see, not having your IP stored greatly increases your privacy, as nothing you say can be traced back to you.
Anonymous IDs offer a great deal of privacy to the average person, but if someone with authority is after you specifically, there is always a way to trace you. Regardless, if you post illegal content, your anonymous ID will be moderated.
It is done automatically for you. Whenever you make a new post using an anonymous ID, any posts made by it over 24 hours are no longer associated to an ID.
Yes. As a matter of fact, anonymous IDs were created with proxies in mind. Since moderation is done at the ID level here, and not through the IP, we do not need to ban all proxies similarly to what other websites do.
As many as you want. You can even share them with others, but that would cause you to also share posting cooldowns with anyone else currently using it.
Yes, but then it wouldn't be anonymous anymore would it?