LittleGreenDots, I have moved your post to this forum. If at anytime someone who knows more than I do about malware thinks it should be moved back to AII it can be continued there.
Do you have ANY Comcast software installed? Constant Guard Protection Suite, Xfinity Toolbar, etc? Comcast does not have a stellar history with branded software.
The Constant Guard portion of the suite can cause system slowdown, as can the toolbar.*side note* If you have Comcast Easy Solve get rid of it. Despite the name it solves nothing.
What is the make and model of your modem? There are Comcast modems that are end-of-life. These EOL devices will also impact speed. You can check to see if your device is EOL here http://mydeviceinfo.comcast.net/
When the page opens check Show End-Of-Life Devices.
If your modem is not EOL, you don't have any Comcast software, and malware is not indicated I can refer you to Connection Experts at the Comcast Help Forums who will be able to look at signal levels and other things to determine if this is a Comcast issue.
Edited by Queen-Evie, 07 December 2012 - 09:46 AM.