Advertisements on web are a most common thing now a day, but many don’t know the fact that some ads are a form of virus! Recently there were reports that people are seeing ads on the one of the largest website, Wikipedia. The site is known to share many valuable information at free of cost and the site is also known for not showing any ads. The site runs on donations and some time to time campaigns.
Wikipedia also mentioned in their official blog that
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 for an example) or anything but our fundraiser, then your web browser has likely been infected with malware.
The ads which you see on Wikipedia are because your computer is virus infected. Its highly recommended that you get the latest update of antivirus and scan your computer.