When the movie starts they show everybody opening the box on the computer to reveal their invitations, which seems alright, when Allison opens hers and discovers it says no guests Derek is able to get right on and get his own invite, which I don't think would actually work.

For one he never logs into a different account, and since he used Allisons computer his IP address would show up as the same as hers whether or not he is logged into his own account or not. Seems pretty sloppy to me and also something that the people responsible for the website and party itself would check for to make sure nobody cheats.

I think that the invites could have been handled alot better, all they have to do is print them straight from the computer, what's to stop somebody from printing out dozens of them and passing them out? Hardly a good way to keep this supposedly "secret" party an actual secret. Of all the different plot holes in this I think this one bugs me the most, maybe it is just because Im a bit of a computer nerd, but I hate how Hollywood seems to know nothing about how computers or the internet actually work