So I'm a poker player. I first heard of Bitcoin when it was at about $5.00, because of online poker. I ignored it and didn't research and really learn about it until the Dec 2013 peak. I'll be honest, the initial intrigue to me came about from all of the "get rich quick" stories, the famous $10M pizza order, things like that. I bought a good chunk at several different times, during and after the MtGox stuff was playing out. But, until recently, I never really used it for anything, never even transferred from one wallet to another.

I don't intend to install complicated software on my computer. I'm certainly capable of diving in, doing things the hard way, and learning how to do it this way, and I certainly appreciate the beauty of the fact that Bitcoin doesn't require the trust of a third party. But what has got me super-re-intrigued again was when I decided to use GreenAddress to receive a transfer of coin. I promise you that I have zero affiliation with that company, and I'm not here to spam or advertise. I researched different online wallets; someone had posted a link to a site that lists the comparative differences between the popular wallets (maybe someone can post that link again)...

What I'm trying to say, in a long way here, is that by using this wallet, I finally see, in a tangible way, the amazing and simple utility that Bitcoin can have. Sure, everyone on here talks about all these complicated nuances of the way it technically works, argues over an understanding of the intricacies, but the bottom-line, for most of the remaining potential market, the future users of Bitcoin, it has got to be simple-to-use, and it has got to have a high perceived sense of security.

It appears to me that GreenAddress has gone a long way to attempt to provide a high sense of security, utilizing the multi-party addresses, the ones where the address starts with a "3" instead of a "1" (maybe someone can explain better than me), and this "nLockTime" which gives you sole access to your coins if GreenAddress goes away.

So, what I am wondering, and hoping someone can further explain to me, what are the basic risks to leaving any relatively significant amount of coin in an online wallet, such as GreenAddress, for any long period of time? Is the risk someone hacking into their servers and gaining access to your coins? Does this multi-party address resolve that concern? Is it the risk of GreenAddress having fraudulent internal compromises? Is it the risk of them no-longer being around in the future? I totally understand that the safest way to hold coin is to have a "paper wallet", but what are the specific... or what is the most likely way that an online wallet would be stolen, my private key exposed?