Online virus scanners can be useful as a supplementary tool, providing a second opinion on suspicious files. They work by uploading files to be scanned on cloud-based servers, which might use multiple antivirus engines for comprehensive detection. However, they don't offer real-time protection like installed antivirus software, so they're best used alongside traditional solutions. Privacy can be a concern since files are uploaded to an external server. It's essential to trust the provider and check their privacy policy. For sensitive files, use offline scanners. Have you found any specific online scanners you're considering?