According to Saurik, the guy behind Cydia, users jailbroke about 18 million iOS devices before the recent iOS 6.1.3 update fixed the exploits. We already know that evasi0n is the most popular jailbreak in history. This number just gives us a better idea of how popular it was.
The jailbreak launched in early February, and within a week reached 7 million downloads. By the end of the month, 14 million users had downloaded the jailbreak. Apple updated iOS to 6.1.3, and that patched the exploits. Apple credited the evad3rs jailbreak team with finding four of the six holes patched with the update.
It’s also said that at least one exploit is still open. The team also keeps several other holes on backup, and keeps them secret, so that they can exploit those when Apple releases an update.