I asked this question on Avast official forum but got no response. I do not blame them because the problem is obviously more related to the Dropbox and Skype than Avast. I use Avast antivirus, Skype and Dropbox with Dropbox Folder Sync which is third party addon for Dropbox. When using Skype I noticed that Avast IM Shield scans some file on this address: C:\Users\Username\AppData\Roaming\Dropbox\shellext\5202b8cd It is very strange to me but I have no enough knowledge and experience to be able to assess what is going on. Why IM Shield scans files related to my Dropbox? Is this normal? My computer is clean according to Avast and MBAM. Does anyone have any experience on this or an idea of what it is? Thanks.