Here is your answer:
As per Skype website:
"Why are there advertisements for other companies in Skype?
Occasionally, you may see advertisements for other companies in Skype (if you're using the free version of Skype). Advertisements help keep Skype free for millions of users, and these advertisements will not disrupt your Skype experience in any way.
If you have purchased some Skype Credit or a subscription, you will not see advertisements for other companies in Skype.
To provide ads that are of greater interest to you, we may use non-personally identifiable Skype profile information (including profile information from a linked Microsoft account), such as age, gender, country of residence and language preference, as well as other information Microsoft Advertising collects outside the Skype software. If you do not want to share this information with advertisers, you can change your privacy settings.
If you opt-out, you will still receive advertisements based on your country of residence, language preference, and IP address location, but other targeting information will not be used."
link to this article: https://support.skype.com/en/faq/FA10942/why-are-there-advertisements-for-other-companies-in-skype
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