 Susanna asks, how safe is a mobile wallet, since our mobiles are constantly using the internet nowadays? Are mobile phones considered a safe option if one does not own a cold storage wallet? Well, Susanna, the truth is that in my opinion, smartphones are generally more secure than the average desktop. This is a very broad statement. What I'm saying is that the average modern, properly installed and updated mobile phone or smartphone operating system is more secure than the average modern desktop. The reason for that has a lot to do with the integration between hardware and software, special hardware for security that exists on smartphones, the way updates are delivered, and the difference in the use model. So on your smartphone, on average, most smartphones, you do not have root access, users do not have root access to the operating system. Yet most desktops nowadays, users have root access to the operating system, which means that when they access the internet, and they access the internet through a browser, and these very big, complex desktop applications that they install willy-nilly from all over the place, malware can easily get in, and once it gets in, it has administrator access to the operating system, and can backdoor the operating system very effectively. So, are mobile phones secure? They're more secure than the average desktop, the average mobile phone, especially recent versions of Android and iOS, on modern hardware, and properly updated versions of those operating systems. Now, is it better than a cold storage wallet? No. Hardware wallets are more secure, because they have a much, much smaller attack surface. They are special purpose devices designed to do one thing, and only one thing, and that is to securely hold seeds. They're not connected to the internet, and they have a very narrow interface through which the operating system can talk to them over USB. That makes them a lot more robust from a security perspective. But if you don't have a cold storage wallet, then a smartphone is certainly much better than a desktop wallet, and much better than most custodial exchanges, where you have third-party risk. Susanna follows up with, what are the proper protection steps to take when creating a mobile wallet? Well, first of all, make sure that your smartphone is properly updated, and you follow the manufacturer's software updates as they come out. Secondly, make sure you actually install the real mobile wallet software. Do not go downloading a package from God knows where. Make sure you download the correct application from the authorized app store, and there are quite a few attempts to impersonate, or to forge, effectively, popular mobile wallets. So make sure you're downloading the right one. Generally speaking, you can see from the number of downloads, users, and reviews which one is the correct one. When you set it up, set up a pin on your smartphone itself. Set up a pin, make sure that both pins are strong, and they're not the same. Use the encryption capability of your smartphone, so that its storage system is encrypted in full at all times. Set it up to lock and remain locked, and require a pin or passphrase to unlock your smartphone. Do not bypass the passphrase locking mechanism by convenient things such as face ID or fingerprint ID, because you can be coerced into unlocking your phone that way. Use the secondary pin function to lock the wallet itself, and if your mobile wallet has the capability, make sure that the pin also protects from opening and seeing the balance, not just sending out the cryptocurrency. In case I have installed a wallet app on my Mac, which has been infected without me noticing, will a hacker be able to retrieve and reveal my private key, already known to the wallet, and previously generated by the get new address command? Eduardo, yes? The moment you type in your passphrase and unlock that wallet, that bitcoin is gone, just as easily as that. In fact, if your passphrase isn't very strong, they can even take the wallet and brute-force the passphrase. But the moment you type in the passphrase, for sure that wallet is compromised, because it's very easy for an attacker who has access to your operating system and has infected it, can do all kinds of things that put them essentially in the middle between your keyboard and your operating system, or your keyboard and your bitcoin wallet application. They can capture the passphrase as you're typing it, and if they have a copy of the wallet, they can then unlock it on another computer, do a transaction, and send it away. Or they can even backdoor the wallet itself and wait for you to type in your passphrase, and your wallet simply creates a transaction that sends all the money away. This happens quite often. It's very difficult to secure a general-purpose operating system such as MacOS. Simon asks, I have a laptop with factory reset, and I intend to never go online with it. In case I want to sign transactions with it, I need to install software such as my Ether wallet. If I copy the my Ether wallet's client script onto a USB stick and put it on my offline laptop, will it be compromising my security because the USB drive could contain some sort of malware? Yes, it will. USB drives can transmit malware, and a factory reset laptop isn't necessarily malware-free. There is malware that can infect firmware, BIOS, and other low-level devices that cannot be removed through a factory reset. There are vulnerabilities inside the hardware, as we've discovered recently, with Intel and AMD processors, or pretty much any CPU processor. Again, a general-purpose computer, remaining offline, is not easy, and connecting it to a USB drive compromises your security. Now, is this better than running my Ether wallet on your Windows 10 online machine that you use to browse all kinds of questionable websites? Yes, it is better, but it's not foolproof, and it's pretty difficult for the average person to do. Again, buy a hardware wallet so you can actually achieve security in a way that's much better than pretty much anything else you can do on your own. Second question from Simon. How would I get the signed transactions from the offline air-gapped laptop to an online client for propagation would I have to type it in manually? Again, see, this is another one of those problems. One way you can do it, and we've seen this with air-gapped systems, is to display a QR code on the screen that contains the transaction, scan that from a smartphone or web camera from another computer, and that way transfer the transaction to the online system from the air-gapped system. Again, this is the kind of operation that becomes technically very complex, and most people can't pull off securely. Hardware wallet versus Glacier protocol. Do you think the Glacier protocol is a good alternative to a hardware wallet? Silver says, Glacier protocol is a step-by-step protocol for storing Bitcoin in a highly secure manner, but has not been widely tested by the global community. Would you recommend similar processes in addition to storing your key on a hardware wallet? I don't recommend that, and the reason I don't recommend that is because, while the Glacier protocol is an interesting approach, and it's a detailed and step-by-step instruction on how to build, what is known as an air-gapped offline quarantined, or whatever you want, a machine that hasn't touched the internet and never touches the internet. This is the kind of technical document that requires a lot of expertise, expertise in command-line and operating systems, and it's very easy to do it wrong. If you do it wrong, then you've exposed yourself to a number of risks which can then lead to your funds being compromised. I think for the vast, vast majority of users, and what I mean by that is, all but maybe a few thousand people who are involved, out of the 25 million people who own cryptocurrency, maybe two-three thousand people, can actually implement something like Glacier protocol effectively and securely, without messing it up, and actually know what they're doing and do it securely. For the vast majority of people, it's way too complex, and a hardware wallet may not be as secure as a perfectly executed implementation of Glacier is, but maybe it's 95% as secure, and yet it is far, far easier to do and to do effectively. So, in security, it really, really matters how usable a security mechanism is. From an operational perspective, whether you can execute the security required, execute it correctly, and operate it. There are a few other considerations as well. One of the critical considerations is, how do you ensure that your heirs or dependents can access your funds if something happens to you? Again, the more complex and custom and esoteric the technique you use, the harder it's going to be for anyone to figure out what you did and help your heirs access your funds. So, generally speaking, while I think Glacier protocol is interesting and I can implement Glacier protocol, in fact, I have built air-gapped computers, and I did build air-gapped computers as a security professional for years, back in the 90s. It's hard to build an air-gapped computer correctly. Nowadays, we know that a lot of the hardware that's in your average laptop has a ton of vulnerabilities. We also know of all kinds of exfiltration techniques that can be used on laptops, including ultrasound and things like that. So, to really, really build a properly air-gapped computer, you have to go in there and quite heavily modify the hardware, at least strip out a lot of devices, including microphones, speakers, infrared receivers, Bluetooth connections, wireless connections, wired connections, glue shut the USB ports, and all of that stuff. And if you can do that, maybe you can build an air-gapped computer. For the vast majority of people, that's what a hardware wallet is. And even despite, you might hear, vulnerabilities being discovered, it's actually quite difficult to exploit those vulnerabilities without fiscal access to the hardware. And it's still far, far easier for the vast majority of people to implement, and less expensive, to implement a hardware wallet. So, I recommend a hardware wallet. If you want to try and play with something like Glacier Protocol, be my guest. At the very least, it's a great learning opportunity. You're going to learn a lot about security, about Unix command line, about playing with hardware and building operating systems securely. Great learning opportunity. But for the vast majority of users, it's not really relevant.