what's happen to this client?

M/4.0 (c; I 5.0; W 98; DigExt; M/4.0 (c; I 4.01; W 98))

[Xuefer]

Mozilla/4.0 (c; MSIE 5.0; Windows 98; DigExt; Mozilla/4.0 (c; MSIE 4.01; Windows 98))
in my log

it made my version detecting script crazy!
what's happen to this client?
it is said his using windows98 3rd version(3rd should be 2nd with some other fixes)

i don't yet get info which use js to detect version

[korkus2000]

Are you sure it isn't a spider?

[Xuefer]

yes i'm sure
i chatted with the user
i don't know what exactly version he has
and how i comes