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I can have a few others running but when I get ready to run a new instance of Firefox in a sandbox I get a message that explorer has crashed and lose all my open explorer windows. Perhaps a conflict with one of the other utilities/drivers/programs running in the background. One minor problem is it seems to cause my explorer to crash every now and then when I try to invoke a sandbox on my 64-bit system (Win 7). I'm glad I paid to have use of all its features and can't imagine being without it.
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Although Shadow Defender does take up a small amount they seem to have some algorithm that prevents disk usage from becoming excessive. The "free" programs will "eat up" your disk space and some change your MBR. Deep Freeze was my favorite but they have an annual fee now.
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Although not free it more than makes up for the cost by being low maintenance. My preferred program to avoid problems you described is Shadow Defender.
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