I had a similar problem, which was after a night of hitting a bunch of Runner blogs, so I figured it was a virus.
I had Norton at the time, and ran a scan but it found nothing. I downloaded several free trials of AV, but the only one that found anything was cyberdefender, and it found 2 viruses on my computer.
It was about $40 to get the full version, which is about what it costs for others, and it came with a money back guar so I figured why not?
Anyway, it fixed some of the issues but not the ctrl alt del problem.
It comes with a 24 x 7 call center, which I called and they were really helpful and told me that since I installed the software after I got the virus that they would need to fixed by remote access.
5 minutes later it was done and the system was clean and on reboot, the ctrl alt del problem was gone.
Since then I have gotten a pop-up every now and then saying something is attacking my computer, and I click the button and it is blocked. Easy to use and I am happy with it.
JMHO