It's not a virus/infection. TYPO3 is a wide spread HTML/PHP based content management system (CMS) which is used e.g. by many professional website creators and it can also be used for building any kind of cross-site information pages, like the one you'd see in this particular case. The error message you see could be triggered by the CMS temporarely is prevented from loading another component, not a big deal.
Typo3 is not installed on the client system, it is installed on the server where the information displayed within the page is coming from and where the page's sources are managed (just like WordPress or Joomla).
Not sure, if it was a temporarely server failure then the end user could do noting but wait. But it also may be some kind of network thingy on the end user's system, a fire wall, a virus scanner, anything which pretends content from an external server to be loaded properly.