why does my scan only take 50 seconds

I have Webroot on a brand new pc, ever since the install the scan only takes 50 seconds. It starts at 6%, then at 11% it jumps to 71%, then from 81% it jumps to 90%, then it jumps to 99% and done. I haven't ever seen a scan do that unless it had corruption or was infected. When I installed Webroot it got infected and wouldn't clean itself up, so I uninstalled it(but it didn't completely) and cleaned it using other means and reinstalled it. I searched for an uninstaller prior to reinstalling but the site wouldn't show one and it said a simple reinstall would correct the partial uninstall. I have a feeling it might be having issues. I have done malware cleaning and it comny help is much appreciatedes up clean but I did have it detect 32 pieces of malware while I was expanding portable apps platform. It could have some infection on the pc but it is coming up clean with Malwarebytes, Hitman Pro, Roguekiller, Kaspersky, FixItStick(My girlfriend bought it for my B-Day so I am obligated to use it since she spent $ on it) . I was thinking maybe in the registry but it doesn't really have any performance issues exept the last 3 days chrome would take forever to register the keystrokes I typed but I looked into it and it was due to a few browser extensions that popped up after letting my 8 year old nephew watch youtube the other day, I deleted them. I don't think he clicked on any of the ads other than to close them. I taught him why he should never click on anything but the x on those but he is 8 and with that in mind he is in that denying everything phase so maybe he did. Any help is much appreciated.