On 6/6/2011 15:30, clipka wrote:
> You need an on-demand scanner though, lest a program opens a file that
> wasn't there when you last had a chance to check it.

Or you have a USN journal. :-)

But yes, if you want to be sure, an on-demand scanner is necessary. It's 
just not a good idea to have it as the first and/or only option.

> So in the sense of "total computing & I/O time spent for virus scanning",
> on-demand may be the worst - but "felt" system speed is not measured in such
> ways.

Yep. In those specific scenarios, where you suddenly add a bunch of files to 
the file system *without* them passing through RAM as you do so, on-demand 
works well.

> Also note that even if a file has been scanned and hasn't changed, the virus
> database may have;

Also a good point. As I said, on-demand should be the last resort, not the 
first. Background-scanning while the screen saver is on of all executables 
when the database changes or when they're written is far more efficient than 
actually blocking a person's access while you scan an entire file. Managing 
to do the scan as part of the VM paging would be even better, but that I 
imagine would be hard to do.

-- 
Darren New, San Diego CA, USA (PST)
   "Coding without comments is like
    driving without turn signals."

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