Virus Warning when installing Skype

AVAST stopped working 8/Feb.

So I re-installed OS Win7 and AVAST, but now, Skype installation is blocked with virus infection warning:

win32:Evo-gen [Susp]

Is Skype infected or is a false positive??? could you explain why this false positive or just fix it please???

Thanks in advance, and Best Regards

PD.: Seems to be fixed. Thanks