Apple just released a new iOS update with version 4.3.4. Apple does not directly disclose what security issue they fixed to not give to much away to hackers. It is though clear that this update is aimed at the recent browser based easy jailbreak. Obviously the same security hole could be used for much more evil things. So if you are not into jailbreaking updating to 4.3.4 makes sense.
The browser based Jailbreak from Dev-Team called Jailbreakme is pretty popular. A couple days ago Dev-Team sent a tweet saying that over 2 million have jailbroken their iOS device via their service. That is quite a lot and something that Apple needs to keep in mind. A lot of iPhone users like their iPhone open.