In this case, leaked means...
UbiSoft gave the latest patch out to beta tester's to test. When you are beta testing somthing, you can not distribute it, and you should be the only one using it. What happened here is one of the beta tester's started spreading the patch around, while he was supposed to be testing it. One person put it on there server, then 1000's got it. That's what a leak is, anyway, the offical 1.10 (for Il-2) is due out monday, but if you can't wait, download the leak.