If avast can detect adirka.exe but can’t remove it that could be because it is 1) in use, 2) in one of the system folders, both of which are protected by windows.

If you have XP or Win2k, you could enable a boot time scan. Right click the avast icon, select Start avast! Antivirus, Menu, ‘Schedule boot-time scan…’ Or see http://www.digitalred.com/avast-boot-time.php

If it continually returns then there are other elements to the overall problem, and using the programs suggested by Spiritsongs should hopefully detect what is restoring it.

A google search for adirka.exe returns many hits, this is just one of them, http://fileinfo.prevx.com/adware/qqf54281124249-ADIR36364162/ADIRKA.EXE.html