ClamAV found infected files on Ubuntu server, what do I do now?

Do these files represent a security problem? Yes.
Will deleting them fix the problem? No.

You've been hacked. Judging from the location of these files, somebody found an exploit in a web script you were running, and they've managed to download these applications. These have allowed them to go on and install more junk which is sending out spam. Hence the blacklisting.

There is no easy recovery from this. This install is compromised trash.

Rescue your data off it, and then work out where the breach was before you put it back online. You cannot skip this and that might involve hiring a professional to pick through your setup, but if you don't find the ingress point, and you just push the same websites back online, you're going to get hacked open again.