Question : virus problem

have had a virus issue with the windows security alert virus since the 5th of JULY.I have  several machines with different customers that this thing has showed up on and i am having a problem keeping it off.So i have to wonder am i getting rid of it totally.I have had success running combofix and malwarebytes in the past but it seems this thing has gotten a little tuffer.the machine i am on now had a rootkit ran combofix it done its thing and then i ran malwarebytes it found nothing.machine appeared to be ok.customer calls back in a couple of days says its on there again.I could use some help in getting rid of this thing for good as i have several customers with the same thing.tools used combofix,malwarebytes,sdfix,kapersky tdss removal tool.I am missing something obviously thats coming back to bite me.have hijackthis on machine if u need to see a log.
Thanks in advance

Answer : virus problem

There is a proxy present, possibly hidden somehow:

R1 - HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings,ProxyServer = http=127.0.0.1:5643

Scan that machine with Hitmanpro
http://www.surfright.nl/en/hitmanpro