I contacted both Symantec and Microsoft about this problem, and they both supplied useful information. They were also mostly in agreement that, as Symantec puts it, the virus identification "was a false positive." In other words: There is no virus in Win2000 Service Pack 1. According to Symantec, the problem occurs when the Microsoft Office plug-in and Norton AntiVirus 2000 version 6.0 (but not Norton AntiVirus 2000 version 6.10.20) are active during the service pack setup. Symantec is readying a patch, but there's also a workaround described