I have understood your problem, not worry though as i shall try my best to get this fixed. There are couple of questions in my mind related to your computer security issue :
> Do you have any other Antivirus software's installed or did you have any installed earlier.
> You said your computer is infected by Trojan, so there are chances were that Trojan is not letting the antivirus software to install completely / correctly.
> Which is the operating system installed on your computer ( Win Xp, Vista or 7)
> Is your computer up to date. Check this by opening Internet explorer - click tools - click windows update.
> Check if the time / date is correct or not on your computer.
Do get back to me with info to go further.
As I understand from your Post I hope you're using the security program which was provided by your ISP Verizon and Package name is verizon internet secuirty powerd by McAfee. If i am right please try this following steps.
Step 1 : Ran Verizon removal tool use the following link to do that Click here
Step 2 : Ran McAfee Removal tool use the following link to do that Click here
Step 3 : Create New windows test account and try download McAfee.