Malware found in firewall.php

Hi,
today I got the message, that malware might be found in …/wp-content/Plugins/ninjafirewall/lib/Firewall.php.

The actual version is Ninjafirewall WP-Edition 3.6.6 under WordPress 4.9.7. The infected? firewall.php has a length of 21,5 kB and was modified the last at 03.06.2018. The providers scan from today says, the file length is 52kB. The used scanner is Revisum Antivirus.

Now i wonder what to do. Should i run the file like it is, or should I use the clean up tool of my provider (that might make Ninjafirewall unusable)

Thanks Hannes