To the best of my knowledge, Avast! is the last FREE real-time/full-time AV which supports W9x/ME. As stated on their "system requirements" page, Avast! is ending support for W9x/ME at the end of 2009: http://www.avast.com/eng/system-requirements-avast-home.html Along with the previously mentioned Clamwin, other on-demand AV products for Win98/ME include: BitDefender 10 Free Edition: http://www.bitdefender.com/bd/site/products.php?p_id=24 "Dr. Web CureIT!", and the Dr. Web "LinkChecker" (scan files before downloading): http://new-download.drweb.com/ (On the lower left of the page, under "Free utilities".) McAfee Avert Stinger: http://vil.nai.com/vil/stinger/