All communication between your computer and Glow is encrypted using industry standard HTTPS/SSL. This is much safer than sending documents by email. We use Amazon Web Services. AWS sets the industry standard when it comes to security, policies, and architecture. We trust them along with hundreds of millions of other companies, including HMRC, AirBnB, and Expedia.
In addition, everyone on our team has two-factor authentication setup for their accounts where possible, which means that nobody can access their accounts (or customer folders) without a security code sent to our mobile devices at the time of attempted login.