I think the concern that some network admins etc 
have had is that the security flaw lies within 
windows. This flaw allows you to access the 
computer in a way you shouldn't be able to such 
as upload the msblaster worm. This being the 
case, I believe that it is -potentially- possible 
( unlikely, sure ) that, knowing this, a hacker 
could exploit the same security vulerability that 
blaster does to compromise the system, upload 
malicious code to the system to capture 
keystrokes etc if they know what they are doing, 
or that they could use the presence of blaster 
detected over an IP range scan to target a 
computer with this vulnerability to hit manually, 
assuming that the worm doesn't specifically 
prevent other things gunning for the same flaw 
when it's present ( it may do ).

As the previous poster said, it's not terribly 
likely that a hacker would target your system out 
of the many. However I think the sysop's concern 
is that this hole was left open and could've been 
exploited by other things than blaster, or that 
the presence of the worm may have been 
an "invitation" for others to use that same point 
of access.

I certainly don't see any harm in resetting your 
passwords etc just in case for peace of mind! :) 
Just my 2c