In my system, virus seems not to remove after successful scanning by Avast 2011

Now a day’s virus becomes more common thread in the everyone’s system and don’t want to leave. I too having problem with these bugs. I scanned my system with Avast and the viruses it found in the voult are as follows:
Win32: FakeAV-CPP [Trj] (found in Temp)
Win64:sirefef-c [Drp] x3 (Found in System32)
Win32:Maleware-gen x6
Windows 7 AV Security is the target of the virus. Whenever it comes back, sys itself as a windows 7 AV Security. I tried deleting it by Malwarebyte, but it is unsuccessful for what reason, I don’t know? It will be very needful if anybody helps me on that issues.

As you have mentioned here that you are working with windows 7. And you are using Malwarebytes to delete the virus. Have your Malwarebyte is updated recently and whether it is registered version or freeware, these things does matter seriously in the system.

If your malwarebytes is updated then perform a quick scan otherwise first update your Malwarebytes and then perform quick scan and wait for the result in the voult, once the scan is finished, see the voult and select all the infected items and press the button of remove it. Then it will prompt for the restart, let your system to be restart and then check for the log. You log file will be saved in MBAM(Malwarebytes Anti-Malware).
If MBAM prompts some file to difficult to remove then it will prompt either message…..click OK and let MBAM proceed with the disinfection process and if asked to restart, do it immediately.

After updating and scanning the whole system, do one more thing……..as you are using widows 7 then…
From the control panel choose the security link, from this window choose administrative tools and then double click on computer management icon, when computer management open then select disk management window. Download aswMBR.exe. Install it and run the scanning. After whole scanning save the log file. Your problem will be solved by the maximum.