The first ever banner campaign had a click rate of 44%

"Joe McCambley, co-founder of The Wonderfactory, a New York digital branding firm, reminded us this week in the Harvard Business Review that he was responsible for the best — and worst — online ad invention the internet has ever seen: The first ever banner ad.
Since it first appeared in October 1994 to promote seven art museums, sponsored by AT&T, to the readers of HotWired.com, the banner ad has earned publishers billions of dollars in revenues.
[...]
The first banner ad was made by Modem Media, a digital agency where McCambley worked, that was later acquired and folded into Digitas.
Of those who saw the ad, 44 percent clicked, McCambley remembers"
Source:  Business Insider, 13th February 2013
Note - I'm assuming that the final sentence means a CTR of 44%, and it's lazy writing, rather than they could track clicks per user rather than clicks per impression back in 1994.