Hotlinkers look out for sites which have no protection. In the same way a car theif checks doors to see if they are locked.
Some firewalls don't like htaccess, and so sometimes images will not appear to someone who is using Norton Internet Security, for example. Which is a downside to using htaccess. But if your sponsor uses a cookie, this may be a good thing and encourage surfers to reduce their privacy settings.
It's always wise to examine your referrer stats on a daily basis regardless of how protected you think you are.
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