I've been running Ubuntu 13 in VirtualBox (Win7 host) for several weeks and it's worked great. This morning, Ubuntu Software Update came up and wanted to install a general update. I didn't look at the details but I remember it was about 60MB worth of updates. After the update, it seems that my Guest Additions no longer work; my screens will not go fullscreen and the mouse is very laggy when it shows up at all (the last few reboots it does not display the cursor at all meaning the system is unusable). I've installed the Guest Additions by way of ISO as well as sudo apt-get install virtualbox-guest-additions-iso. Both succeed (slightly different versions), but neither fix my problems. I'm looking at having to completely rebuild a new virtual machine (this time not Ubuntu) if I cannot solve this issue. I guess I've learned my lesson to simply dismiss Ubuntu Software Updater when it wants to update the system, at least when running in VirtualBox. I imagine others will be running into this problem today as they update their systems; any advice in getting me back up and running would be greatly appreciated.