Commercial products from Bitdefender, Kaspersky, and Norton consistently achieve 99%+ detection rates. ClamAV achieves around 97% — respectable but not top-tier. Commercial vendors update threat definitions multiple times daily. Open source relies primarily on signature matching. For enterprise use, commercial products are clearly superior. For budget-conscious users and specific use cases like mail servers and Linux workstations, open source tools like ClamAV provide meaningful protection. Our detailed analysis includes specific recommendations for each use case and budget level.