My agents and customers see red screens when they try to access URLs that lead to my Zendesk account titled Deceptive site ahead, Malicious or Harmful site, Site contains harmful programs or similar.
Google Safe Browsing flagged one of your subdomain's attachments or webpages as harmful, malicious, or unsafe. When this occurs on your subdomain, it can cause all attachments or pages to be blocked by the browser, and present a red screen error, until a successful review within Google Webmaster tools confirms that malware attachments were removed, or the page was remedied.
Google notifies Zendesk when they detect unsafe pages or attachments. Then, Zendesk removes the attachment and requests a review from Google to get any malware warnings cleared for the affected subdomain.
While Zendesk constantly monitors all accounts for errors and alerts, you are also able to do it yourself by following the instructions in this article: Can I verify my subdomain to be used in Google Search Console?
For more information about best practices on attachments and security see the articles below.