<center>https://upload.wikimedia.org/wikipedia/commons/a/a5/CEX_LOGO_COLOR.png</center>

>As you know, we at [CEX.IO](www.cex.io) always work hard to improve security of our platform even more. Today, we are thrilled to announce that we are going to change current Bitcoin addresses to multi-signature Bitcoin addresses, offering an extra security layer for you.
Considering this upcoming update, please pay attention that your Bitcoin address on [CEX.IO](www.cex.io) will be changed to a multi-sig address on **October, 3rd**. Considering this, please make sure to check out your new address, beginning with a “3”, in profile and use it to deposit funds to your account, starting from Monday.
Thank you for choosing [CEX.IO](www.cex.io)!

It is a great thing that more exchanges are trying to make their services safer.
I am curious whether [CEX.IO](www.cex.io) is implementing multisignatures all by themselves or they use 3rd party signer like [BitGo](https://www.bitgo.com/). As it turned out [BitFinex got hacked](http://blog.bitfinex.com/announcements/security-breach/) and they were using multisignatures with [BitGo as a partner](https://blog.bitgo.com/bitfinex-and-bitgo-partner-to-create-worlds-first-real-time-proof-of-reserve-bitcoin-exchange/). Something went wrong there, so just implementing multisignatures is not enough and could just dull your vigilance. 
<center>**You have to implement it RIGHT.**</center>

What is a MULTISIGNATURE Cryptocurrency address?
>A multi-signature address is an address that is associated with more than one private key. The simplest type is an m-of-n address - it is associated with n private keys, and sending bitcoins from this address requires signatures from at least m keys. A multi-signature transaction is one that sends funds from a multi-signature address.
<center>https://bitcoin.stackexchange.com/a/3729/4334</center>

So you can have 2 of 2 mutisignature address. It means you have 2 private keys for this address. To make a transaction you have to sign a transaction with those 2 keys. You can have one key, your wife second one and transaction is processed only if 2 of you agree to it.

In Bitcoin multisignature addresses begin with 3, but addresses beginning  with 3 don't have to be multisignature addresses. It is just an indication that it is a Pay-to-script(P2SH) address. Multisignatures are just a form of Pay-to-script scripts. 
Want to know more about about Multisignatues and P2SH?
You can start here: 
https://en.bitcoin.it/wiki/Multisignature
https://en.bitcoin.it/wiki/Pay_to_script_hash