There are a handful of scattered examples. Fortunately because of how signing works it makes malware that is signed incredibly easy to detect, since by the ver

There are a handful of scattered examples. Fortunately because of how signing works it makes malware that is signed incredibly easy to detect, since by the very nature of the signature the malware's contents cannot be altered. Plus signing is costly, and that within itself can make malware attacks uneconomical. It also makes getting a signature rather complex since you need fake identification and payment to avoid being carted off by the authorities. Overall signing requirements are a huge net win for the "good guys." And while it isn't a hard security boundary, it is a damn effective one in the real world.