Some examples detect malicious activity on a computing device. A processor in kernel mode detects an event on the computing device. The processor provides a validation request on a kernel-level bus. A bidirectional bridge component transmits the request to a user-level bus. The processor in user mode determines that the event is associated with malicious activity and provides a validation response on the user-level bus. The bridge component transmits the validation response to the kernel-level bus. In some examples, the processor in user mode receives security-relevant information from a system service of the computing device, and analyzes the event based at least in part on the security-relevant information. In some examples, the processor in user mode receives a security query, queries the kernel mode via the bridge component, and responds to the security query indicating that the data stream is associated with malware.