During normal browsing with this extension installed, no data is sent anywhere. The only way that data will be sent to an external server is when the user deliberately asks to scan a given URL or file download with the extension. In such cases, the URL containing the file download, the URL in the link that should be scanned or the site being displayed (depending extension button pressed by the user) will be sent to VirusTotal for scanning.
External services privacy policies:
VirusTotal fully respects your right to privacy, and will not collect any personal information about you without your clear permission. Any personal information which you volunteer to VirusTotal (e.g. by signing up to VT Community, sending a given file or URL, commenting on scanned resources, or making use of any other Service) will be treated with the appropriate standards of security and confidentiality, strictly in accordance with the Spanish Law 34/2002 on Information Society Services and Electronic Commerce (hereinafter LSSICE).
Information volunteering implies accepting the transfer of this information to Spain and/or other countries for storage, processing and use by VirusTotal. As part of providing you the Services, we may need to provide you with certain communications, such as service announcements and administrative messages. These communications are considered part of the Services and your VirusTotal community account, which you may not be able to opt-out from receiving.