The bigger question is why do all these files have the educational stamp on them?
If they were created by an educational product, then this thread is asking us to help you break the law.
If they were truely created by a commercial product, how did they all get infected?
If it was someone in your office screwing them up, I would take the cost to fix them out of thier pay, or make them fix them on thier own time to keep thier job...
Too harsh?
First, at least in California (this is most likely true throughout the entire U.S. though), it would be illegal to take it out of their pay or make them fix it on their own time, even if they did this deliberately, which I doubt anyone did, considering how easy it is to get anyone infected. Now, if they did it deliberately, you could fire them and then sue for damages, but you can't just take it out of their pay without a court order. I only mention this because I have seen too many people jump on this idea and it can get companies into deep, deep trouble. For example in California, last I checked the penalty for doing this is 3 times what was taken out. Additionally, the last I checked in California, if a paycheck or any portion of it is late (not paid on the agreed upon date) (there are a few exceptions to this, but not many), the company must pay 8 hours per day that it is late, which is where the 8 hours per day comes from, if a person is salaried, then it is the equivalent of 8 hours, based off of a 40 hour work week (not including, holidays, vacation time and weekends). So, you can imagine that this could be a very costly mistake for a company to make and I would hate to see any company have to eat that kind of expense. So before considering doing something like this, always check your local labor laws.
That being said, it is actually very easy to get infected by the educational stamp, it is basically a virus. If you have a drawing with an Educational stamp on it, any other drawing that it touches in any way, shape or form, this includes, but is not limited to being xRefed in, being brought in as a block. If you have other drawings open and then open a drawing with an educational stamp, the other drawings will be infected if you save them. For this reason, I will not allow drawings with an Educational stamp to be saved to our server and the email that contains them is deleted immediately when we find out it's there, if it's on an FTP site all information for accessing that FTP site is deleted from all email accounts, etc. Yes, this might be overboard, but it's truly the only way to ensure that your other files do not get infected.
NOTE: AutoCAD 2014 SP1 (and presumably newer versions) does not do this, but I still won't allow drawings that I know to contain an educational stamp to be saved here, just to be safe.