If you have access to the nmap tool, you can check to see if your server is running an open, unsecured HTTP proxy by running the following from a remote location:

sudo nmap -sS -sV -p 8080 --script http-open-proxy.nse X.X.X.X

where X.X.X.X is the IP of your server.

Example:

# sudo nmap -sS -sV -p 8080 --script http-open-proxy.nse X.X.X.X

Starting Nmap 6.00 ( http://nmap.org ) at 2014-04-22 17:05 UTC

Nmap scan report for host.domain.com (X.X.X.X)

Host is up (0.078s latency).

PORT     STATE SERVICE VERSION

8080/tcp open  http    Apache httpd

| http-open-proxy: Potentially OPEN proxy.

|_Methods supported: CONNECTION

If the script returns "Potentially OPEN proxy." you can then check to see if it is a open proxy that does not require authentication with:

http_proxy=http://X.X.X.X:8080/ curl -4 -s http://nyc2.mirrors.digitalocean.com/tools/open_proxy_check.txt

where X.X.X.X is your server's IP address

If you see a message saying "If you are seeing this while running the open proxy text, your server is an open proxy." then you are running an open proxy that anyone in the world can use to connect to any website. This is not a good situation, as it means that cybercriminals and other malicious entities can hide their activities and make it seem like their web connections are originating from your server, and you should secure it right away.If you are running squid, a method of securing your proxy is by using the "acl" feature:

http://www.squid-cache.org/Doc/config/acl/

If you are running Apache, this article may help:

http://wiki.apache.org/httpd/ProxyAbuse

If you have any questions, log into the DigitalOcean control panel, click on "Support" and open a support ticket!