Hello
I used to use boot scan a lot to pick up viruses etc that a normal scan would not detect. However I am now using a 64bit Windows 7 operating system and the option is unsupported.
I wondered how soon (if at all) the Avast! crew will get boot scan functioning on 64bit operating systems as I believe it is an incredibly important tool. ???
Version 5.1 should be released within the next 2 months as to my understanding, and the 64-bit boot-scan is projected to be available in this version. 
Fantastic, thanks for the quick reply.
Glad I could be of help. 
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Stay tuned to the forum for news on the new release.