Web Shield is a unique feature of avast! that enables it to monitor and filter all HTTP traffic coming from the Web sites on the Internet. Since an increasing number of viruses (and other malware, such as adware, spyware and dialers) are being distributed via the World Wide Web, the need for an effective countermeasures has also increased. The Web Shield acts as a transparent HTTP proxy and is compatible with all major web browsers, including Microsoft Internet Explorer, FireFox, Mozilla and Opera.

Unlike most competitive solutions, Web Shield's impact on browsing speed is almost negligible. This is because of a unique feature called "Intelligent Stream Scan" that lets the Web Shield module scan objects on-the-fly, without the need of caching them locally. Stream scanning is performed in operating memory only (without the necessity to flush the contents to disk), providing maximum possible throughput rates.