Wikipedia: If you see banner ads on our site, then you might have a virus
We never run ads on Wikipedia. Wikipedia is funded by more than a million donors, who give an average donation of less than 30 dollars. We run fundraising appeals, usually at the end of the year. If you’re seeing advertisements for a for-profit industry (see screenshot below for an example) or anything but our fundraiser, then your web browser has likely been infected with malware.