Web Security Categories

Malware—Blocks requests to access servers hosting malware and websites compromised through any application, protocol, or port. The malware category integrates the two Talos threat levels untrusted and questionable. Available for both DNS and Web policies. Recommended.
Command Control Callbacks—Prevents compromised devices from communicating with command and control servers through any application, protocol, or port. Also, this setting helps identify potentially infected machines on your network. Available for both DNS and Web policies. Recommended.
Phishing Attacks—Blocks access to fraudulent websites that are designed to steal personal information. Available for both DNS and Web policies. Recommended.
Potentially Harmful Domains—Blocks access to domains that exhibit suspicious behavior and may be part of an attack. DNS policies block this category, however, because this category integrates Talos's questionable threat level, Web policies can only isolate these domains with Remote Browser Isolation (RBI). For more information, see "Potentially Harmful" Security Category.