Our site is built on top of Drupal, an open source web publishing platform used by many large websites, including whitehouse.gov and many institutions of higher learning. We use a reputable managed hosting provider, Pantheon, to host our site and keep it safe from many of the common internet attack vectors that affect websites.
To keep data safe from accidents and hacking, we back up the site each day. This is done automatically by our hosting company.
If volunteers are using our mobile application for Android or iOS, all information is sent over HTTPS.
Additional information about Pantheon security is available here: https://pantheon.io/security
Recommendations for your organization:
Use strong password that is not repeated on other sites, for additional security
Use a secure connection (https) to log in and enter their hours. This can also work with embedded hours forms, as long as the containing site is also using HTTPS.