I Received an Email from Comcast telling me one or more of my PCs are a part of

Okay, so first, let me state how many devices use my Wi-Fi network. 1. My mother's laptop, it runs Windows Vista 32-Bit. I set her up with Advanced System Care 4, Firefox, IE9, MyWOT and AdBlock Plus. I highly doubt it'd be hers, also she has Norton 360 provided from her ISP. 2. My PC, it dual boots Windows 7 and Ubuntu Linux. I've never gotten a Virus on Windows 7 either, as I have MalwareBytes Pro, Advanced System Care Pro, and used to have Norton 360 provided by ISP, but switched it out for Avast! Free Anti-Virus with a license key that lasts until 2038. On Ubuntu, I have Firefox 4 with MyWOT and AdBlock Plus, so even then I am protected. I'm more of a Security Freak though, so I always make sure that my security is up to date. 3. My mother's friend brings his laptop over when he comes, and he's had an adware called "MyWebSearch" in which I found on my mom's PC at one time and removed with MalwareBytes. I also removed it from his PC. I also put ASC4 on his as well. I uninstalled a trial Registry Cleaner on his PC in which is nephew installed for some reason. His Laptop may have been a cause... or... the most likely candidate. 4. My dad's old laptop in which he stopped using because of a Rogue AV, but after scanning with MalwareBytes, it was an easy fix. No problem at all. I dual-booted Ubuntu with it's Vista and it's been smooth sailing. I've never used it's Vista after removing the Malware though, so it could have been a reason for it. I recently overwritten Fedora 14 on the Hard Drive so Vista is no more. It may have been the Vista partition that caused it. But there was another... 5. My Old PC was hit hard by a Rogue AV and then I didn't know how to remove anything. This was around a year ago, I got this PC for Christmas, and I wouldn't be surprised if it was apart of a Bot net, but I recently fixed it up and gave it to my friend because I didn't have enough space to use it.