Alice:
You're going to have a hard time finding anti-virus programs and anti-malware/antispyware programs that work with Windows 98SE/ME. Most all of them only work with Windows 2000/XP/Vista/7.
The technical section of
SUPERAntiSpyware 4.30.0.1004 says it works with all versions of Windows. I personally don't know if it does. Download it and install it and see what happens. It's a very good program and I use it myself.
What is he using for an anti-virus program, and is he still able to get definition updates for it?
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