When you create a link to an another site using the target="_blank" attribute (open in new tab), you can expose your website to performance and security issues.
The other page may use the same ressources than your page and your page's performance may suffer.
The other page can access to informations from your page, using the window.opener property. This may allow the other page to redirect your page to a malicious URL.
To avoid these issues, add a rel="noopener" or rel="noreferrer" attribute to your links using a target="_blank" attribute.