How targeted is Sandboxie by malware creators?

[Conadan]

Have there been any attempts by exploit kits or any other malware to break out of Sandboxie?

If not, is it because of it's too costly or difficult to break out? Perhaps Sandboxie is not large enough to yet be a problem for malware to spread?

If yes, is there any additional settings in Sandboxie to give some extra protection?

I've read the Bromium paper about how they bypassed Sandboxie but that was a few years ago and it was only done for testing purposes.