This rememeber me some years ago I had managed to get in Purdue university on only 1 computer and I expended myself on 30-40 computers to generate rainbowtables that takes 1 year to generates in less than 3 weeks :> But since I got in the news I stopped that due to the risks
Someone hacked purdue - Google Search
But to say short I used to intrude a computer with a 0day MS bug and used to crack the administrator password on the 1st computer and I intruded its network with a bunch of tools like ipcscan etc because he used the same passwd on a lots of computers(very common windows admin mistakes). So yes as soon as you're on 1 computer you can expend yourself but I won't explain each steps, just search around for ipcscan, rainbowtables, etc as long as you're on 1 computer in a non really secured network you can get a few more victims, that would have not been possible if the admin did setup a strong & unique password for EACH computers, but he used the same and boom..
ps: If you're working for federal laws or something like that didnt fount out what I had made on theses boxes and you're reading this message, I had not stoled sensitives students or admins datas, just the admin password to generate my rainbowtables on top noch 3Ghz comps(which were strong CPU 4years ago) in less than 3weeks where it must take 1 year or more on only 1 comp heh. Thanks again for your computers purdues
