Thanks for letting us know. The image that someone was trying to display on that member's visitor page was on a site that has since been taken over by a malicious company trying to cause problems.
We do not limit our members from linking and displaying images from anywhere else online. The problem is, we're 20+ years old, and many of those sites simply don't last that long. When taken over by someone else, they are often repurposed for malicious purposes. Image sites are particularly attractive for this, since people link to them from all over -- and especially forums like ours.
When you let us know you find such a problem, we will remove the offending image and link, and that'll make the warning in the web browser go away. Thanks again.