A fine example is wire fraud. Existing fraud laws didn't really cover it, and innovative criminals made extensive use of the loopholes until wire fraud was criminalized. (For those interested, the Yellow Kid's autobiography is a fun read. )
Same thing with any sort of security hole, really. We'll always have on-line attackers, but that's not a reason to give up. It's a reason to keep plugging holes and improving state of the art.
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