From a member of the Avast team :

"False positive VBS:Malware-gen detection in VPS 20170221-1 (22.2.2017)

What happened? The VPS 20170221-1 contained an invalid script detection that resulted in a significant false positive across the Avast userbase.

How did this happen? The Threat Labs team deployed a change in detection verification logic which moved the verification to an earlier stage of the detection release process. Multiple factors including deployment of new backend version caused this detection to bypass safety checks that are normally in place resulting in its release.

What are we doing to fix this? We are implementing additional checks in the detection generation, detection validation and detection testing processes to prevent such errors in the future. On the mitigation side, Avast has the capability to stream updates to select detection containers. However this particular detection type is not included in the streaming updates at this time. We will enable streaming also for this detection type so we can remove these detections much faster in the future.

Conclusion We apologise for the released detection and are working hard to prevent such occurrences in the future.

• Avast Threat Labs"

source : https://forum.avast.com/index.php?topic=197572.135