Recently wordpress users facing this issue Admin page goes blank after wordpress core version upgrade, Once the wordpress version successfully upgrade it will redirect to wordpress About page contains information about the Latest version and features. When upgrade(manual/automatic) wordpress to a new version it updates both the core files including wp-admin and wp-includes folder andread more  

It is possible to use PHP to check whether your site visitor uses Internet Explorer and output some IE-specific text or HTML/CSS markup In PHP superglobal array $_SERVER there is usually HTTP_USER_AGENT element which contains browser-specific id string