As reported by MacCentral, this comes from the Northwestern University ftp

Disinfectant Retired
Announcement and Press Release
May 6, 1998

I regret to announce that I am officially retiring Disinfectant, our free
anti-viral utility for the Macintosh. The current version 3.7.1 is the last
version. Disinfectant will not be updated for the new Autostart 9805 worm
or for any future viruses, worms, or other Macintosh malware.

I made this decision not because of the new Autostart 9805 worm, but rather
because of the widespread and dangerous Microsoft macro virus problem. I
believe that there are now well over 1000 of these viruses, and many new
ones are discovered every month. They are now a much more serious problem
for Mac users than are the classic Mac system viruses. I simply do no have
the resources to combat a problem which is this huge in scope and

I am aware that some Mac users do not use Microsoft Word 6 or Excel 5 or
later versions, and hence have still found Disinfectant useful. These
people seem to be a minority, however. The majority of Mac users need a
commercial anti-viral product. Disinfectant is not adequate protection, and
hasn’t been for several years. For this reason, I feel that there is little
point in updating the program for the new worm. Doing so would, in fact,
only provide a false sense of security, and result in more harm than good.

The following commercial anti-viral utilities are currently available for
the Macintosh. All Disinfectant users should switch to one of these

Anti-Virus Toolkit. Dr. Solomon’s.
SAM. Symantec.
Virex. Dr. Solomon’s.
VirusScan for the Mac. Network Associates.

I began working on the Mac virus problem and Disinfectant ten years ago, in
the Spring of 1988, when the first Mac viruses began to appear.
Disinfectant 1.0 was released to the public on March 18, 1989. I have been
enormously gratified by the success of the program and its very kind
reception by the Macintosh community. I’d like to take this opportunity to
thank my many users for their support and encouragement over all these
years. I’d also like to express my appreciation to the other members of the
Mac anti-viral research community for their outstanding spirit of
cooperation and public service which has made all of our products possible.

Nine years is a long run for any kind of computer software. It’s time to
move on.

John Norstad
Northwestern University