AVG found a hidden extension, what does this mean?
AVG Free gives the following message: Warning: hidden extension . exe
Some viruses hide themselves by doubling their file extension. For example, the VBS/Iloveyou virus attaches a file, ILOVEYOU.TXT.VBS, to e-mails. The default Windows setting is to hide known extensions, so the file looks like ILOVEYOU.TXT. When you open it you do not open a .TXT text file but instead execute a .VBS script file.
Because of the increased use of this technique we have added detection of the double file extension into AVG Free. Of course there are cases of valid, harmless double extensions, e.g. uninstall.rar.bat, which is part of some installations of the RAR compression utility.