Ask anybody that spends time in the security circles and they'll tell you that every large software project is bound to have a few long-standing vulnerabilities in the code. Fortunately, there are usually a few people who are paid to close up those holes so you, the customer, don't find yourself the victim of nefarious evildoers someday. Like so many before it, the latest update to Android came with a boatload of changes, at least one of which fixes a potentially dangerous vulnerability that can be used for numerous attacks, including a way to acquire root.
In the ever expanding quest for root access on the EVO 3D and its T-Mo cousin, the Sensation 4G, another chapter has unfolded. XDA devs have achieved sticky-temp root on both handsets, which basically means that temp root will now survive reboot. This still isn't permanent root, though, as the SU binaries are not in the default path(s), but instead an alternate location which can lead to some root apps not functioning properly.