The essence of any VPN (Virtual Private Network) is to encrypt the Internet connection. Connecting to the Internet through a VPN, we can protect our online privacy, hide our online activities, and enjoy the safe & anonymous web surfing worldwide. Avast SecureLine VPN (Avast SecureLine or SecureLine VPN for short) is a fast, secure and cross-platform VPN software developed by Avast Software from Czech Republic. It's subscription based and available for Windows, Mac, Android, iOS platforms.

It is well known that Internet is full of tracking software, advertising, and guys who are monitoring and collecting other people's data for various purposes. In other words, as long as it's on the Internet, you can be exposed to risk at any time. In addition, some websites may block or restrict your access depending on the IP address of your location (you must have encountered such situation: a website just shows you with 403 error). In these cases, using a VPN is the best solution at the moment.

UltraSurf (AKA: 無界瀏覽) is one of the world's most popular free anti-censorship and pro-privacy applications, developed by UltraReach Internet Corporation in 2002. It was originally created to help internet users in Mainland China (where the Internet is heavily censored and Internet users' activities are monitored by the Great Firewall of China) bypass internet censorship and protect their online security & anonymity. After that, it became popular in many countries with Internet blockade due to its good usability, fast running speed and unlimited network traffic.

Above all things, you have to know what port forwarding/port mapping is. Port forwarding refers to the mechanism of packets forwarding. Its essence is firewall's configuration strategy. But its function mainly focuses on packets forwarding, in order to achieve the purpose of operating specific packages (IP address parsing and filtering based on destination port number). As a consequence, it is generally taken out as an independent concept.