The following are my current recommendations for maintaining security in Windows 98 and 98SE. Because malicious invaders are capable of interfering with the suggestions contained in my "Clean Boot" procedures, I recommend these programs and procedures be employed first. Still, it may be necessary to set up a Clean Boot, and even then manually kill a malicious process or two, before you can complete the cleanup procedures suggested here. While I try to use Normal Mode Windows whenever possible, some invaders will require running malware scanners in Safe Mode. Many invaders are built to first detect and disable protections that are in place, so that you might, for instance, have to obtain and employ a DOS-boot antivirus like F-Prot or Multi-AV (for this link, IE users may need to take note of the little bar that drops down to request permission to start the download.) Repeated running of scanners, booting back and forth from Safe Mode to Normal, or into DOS Mode--a lot of gymnastics are often required to get to an error-free and nasties-free condition. Once there, however, some user sanity and education--regular "wetware" updating--will *keep* your system healthy.
Update your Antivirus, then run a full scan. For standard, daily-use antivirus, I can only recommend Avast!. I know of no other antivirus that still supports any of the Win98 operating systems, free or paid versions. Avast! has a free version. Then, if you haven't already done so, obtain, update, and run any or all of the Trojan/Parasite/Adware/Spyware cleaners listed farther down. I recommend getting and running *all* of them. They each target slightly different things. Again, be sure you update the definitions they are using to identify crap before running them, each time you run them--which, depending on your surfing habits, should be anything from once a month, to once a week, to once a day, to once an hour if you're really into junkware sites (aka "Free goodies", game sites, fun-places-to-be, etc.)
Tradition has it that firewalls are generally not needed when using simple dial-up modem connections. Alas, this is no longer the case. *Everyone* needs a firewall! For firewalls, the older version of ZoneAlarm 6.5 still works well, and there's also old versions of Tiny and Kerio firewalls available on the internet at various places, but I can't recommend any particular download sites.
In addition to Antivirus and Firewall protection, I consider the following items to be indispensable protection and clean-up utilities. My judgment is based upon their being free (though donations are always welcome!), good, accurate, and safe if handled correctly. See, also, suggestions from MVP Mike Burgess on his site, http://www.mvps.org/winhelp2002/security.htm. More current discussions of Security issues can be found at the Windows Support Center (provided by MVP Jim Eshelman, a true Saint!) More good info can be found at http://www.claymania.com/removal-trojan-adware.html. Note that even though more recent resources on the topic will concentrate on Windows XP and Vista, much of the advice is still equally applicable to Windows 98. Just have to be careful of things like Registry tweaks and similar things and MAKE SURE the advice is Win98-specific.
SpyBot S&D ("SpyBot Search & Destroy") http://www.safer-networking.org/index.php?page=download
Spyware Blaster http://www.javacoolsoftware.com/spywareblaster.html
AdAware SE is no longer being supported, but some have noted that if you can obtain the application and get its last definitions update, it will at least catch things that other apps might not.
PLEASE! Before using any of these products, see MVP Sandi Hardmeier's Site at http://inetexplorer.mvps.org/darnit.html for suggestions and cautionary information about internet surfing, and some important hints about using the above. ESPECIALLY, be aware that HijackThis scans result in a LOT of stuff that you *don't* want to delete. The admonishment to save a log and show it to an expert is critically important advice. Not following that advice can really do some damage to your system. SpyBot's SD Helper and TeaTimer , too, are capable of similar problems, especially if you change default scan settings, or "Immunize". I recommend installing it with none of the extra goodies, and *only* periodically use it to scan for malware. The SuperAntiSpyware free version does not have "resident protection" (protection that runs continuously in the background.) While the Pro version does have resident protection, I'm not familiar with its behavior on Win98 systems and would recommend against its use.
One additional tool that is very helpful in protecting your machine is a HOSTS file. Microsoft MVP Mike Burgess maintains a frequently updated list of bad sites. They may be sites that provide most of the junky advertisements you see in other places, or sites that install spyware/adware, or that, for whatever reason, you shouldn't allow into your system. Using the HOSTS file, you can redirect such addresses to a site that's guaranteed to fail to load on most machines--your own computer.
HOSTS Overview -- http://www.mvps.org/winhelp2002/hosts.htm
Also handy is MVP George Geyde's HOSTS File Manager. You can find it at the bottom of this page: http://dundats.mvps.org/Software/Index.htm
Last but not least, I must repeat that you should see Jim Eshelman's http://aumha.org/a/quickfix.htm for a lot more detailed and expert suggestions for when you think you've been invaded by malware.
Lastly, it is a simple fact that you will soon not be able to find decent protection applications for Windows 9x versions. These types of apps require regular updating both in the program and the definitions, in order to stay ahead of the bad guys. There being so few Windows 9x machines remaining in use, it isn't cost efficient to continue to build Win9x-compatible apps. That's the way the market works.
Gary S. Terhune
MS MVP Shell/User