that time expentancy decreases exponentially in case of win98 fresh install
Win98 is more secure than winXP, Linux and BSD (except for OpenBSD perhaps) by default because it is:
-old and thus unlikely to have specific features being attacked by worms
-feature lacking, it has no damn servers being initiated from the first time you boot

By design it is not exactly secure obviously.
It is easily secured because there are few features to take in account.

as a matter of fact i think that there is only hole in free bsd
FreeBSD has numerous holes.