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That looks like the icon for Adobe Updater alright. You’ll typically find the program Adobe_Updater.exe in a directory such as Program Files\Common Files\Adobe\Update6\
It’s used to control auto updates of programs such as Acrobat, Reader, Photoshop, etc.
It occasionally needs to be updated itself. See for example:
Adobe Updater 6.2 Update
http://www.adobe.com/support/downloads/detail.jsp?ftpID=4509
If in doubt about the legitimacy of the update prompt, check the version you have installed and then go to the Adobe site - perhaps the forums would be a good place - and see if there’e a later version than what you have.
Perhaps it’s not in avast!'s suggested updates list because it isn’t known to be vulnerable to exploits … my guess.