Comodo can let bad malware install. It was in the sandbox, but it's still not a good thing. Take for example the Santander malware. Just because it was running in the sandbox, it would've still sent all your personal details to the scammers if you'd put them in.. You might as well use a decent AV engine such as Norton, Kaspersky or aSquared alongside a dedicated sandbox program. Kaspersky lets you virtualise everything if you wish to with the Saferun application. Comodo is only as good as its user.