Quote from: OROBTC on February 07, 2015, 05:10:37 AM

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When I have nothing better to do, I sometimes browse the blockchain via blockchain.info. Really just to get a better feel for different kinds of transactions and to learn a bit more (some of you know I am a relative beginner who has pretty much had to "learn by doing" and not a programmer).

(Some time ago, I asked bitcointalk about addresses that have a small letter (after the 1) vs. a CAPITAL letter, and I also asked about how a small percentage of addresses have ONE less alphanumeric in their addresses vs. the overwhelming majority of others. The answers I received explained BOTH points very well. Thanks!)

Well, here is another little oddity I have seen recently. A small percentage of addresses (maybe 0.5% -- one in 200 or 300 addresses) start with a 3. One very interesting address that moves a LOT of BTC around (and starts with a 3) is at Block Height 342350 (won by Slush). A LOT of BTC!

There are only some 93 transactions at 342350, so if you want to see for yourself, just drop by and scroll down. That "3" address is the only one I saw there.

Why is it that some addresses start with a 3?

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I guess that a second question is in order. Is posting a public address (like the one starting with "3" at 342350) considered "Bad Form" here at bitcointalk?

Hey, I don't want to cause any trouble around here...

Address starting with 3 is a multisignature address, a address requiring 2-of-3 signatures to be able to be spent. It is an address associated with more than one ECDSA private key. It is usually used as cold storage as it is harder for one to steal 2 private keys compared to 1. It can also be a protection against malware as you could keep the keys on separate computers. Keeping one of the three keys safety is also a good practice, if one of the keys is lost, the bitcoin can still be spent using 2 of the remaining keys. It can also be shared between multiple people, majority of the people can vote and spend the coin.