Malware?

Hello to anyone,
my host provider informed me with this message:

Hello,

ImunifyAV scanned your websites automatically for malware. At least one of them is infected and needs your action:

reteinformatica.biz 1 file infetto
/wp-content/plugins/w3-total-cache/inc/lightbox/support_us.php

negozio.reteinformatica.biz 1 file infetto /wp-content/plugins/w3-total-cache/inc/lightbox/support_us.php

Remove the malware with one-click

Best regards,
Plesk and ImunifyAV Teams

Same thing with another site I have with other domain.