What is a web filter?
Definition
A web filter is software or a service that blocks or allows websites based on rules, such as known malicious addresses or unwanted categories of content.
- Category
- Security
- Also called
- web filtering, URL filtering, content filter
- Last updated
A web filter checks the page you are trying to open against a set of rules and either lets you through or blocks it. CISA describes URL filtering as a control that permits or denies access to a web page when someone clicks a link, built on allow-lists (only these sites), block-lists (never these sites) or both. Its Trusted Internet Connections guidance describes content filtering as detecting unapproved content and removing it or denying access.
Where you meet one
- At work or school, where the network blocks gambling, adult content or known malicious sites.
- At home, in a router setting, a DNS service or parental controls that stop children reaching certain sites.
- In your browser or security software, which warns you about pages flagged as phishing or malware.
An example
You get a text with a link to a fake delivery page. If a web filter has that address on its block-list, the page doesn't load and you see a warning instead. That is the main security use: it cuts off a click you shouldn't have made.
What a filter can and can't do
A filter only knows what it has been told about. A brand-new scam site may not be on any list yet, and a determined user can sometimes get around a filter with a VPN or a different DNS setting. It also can't protect you from handing over details on a page that isn't flagged. Think of it as one layer, not a guarantee.
Filters can also see where you browse. At work, the organization running the filter may log which sites you visit.
Web filter vs. related terms
- A firewall controls network traffic in general. A web filter looks at web addresses and content.
- An ad blocker hides adverts and some trackers in your own browser. It isn't there to enforce an organization's rules.
How to protect yourself
- 1
Turn on safe browsing in your browser
Chrome, Edge, Firefox and Safari warn you about known phishing and malware pages. Leave those warnings on.
- 2
Use a filtering DNS service at home
Many routers let you set a DNS service that blocks known malicious domains for every device on your network.
- 3
Don't rely on it alone
Don't enter passwords or card details after clicking a link in a text or email. Open the site yourself instead.
- 4
Know who sees your browsing
On a work or school network, assume the filter can log the sites you visit and keep personal browsing on your own connection.
See where your personal data is exposed
Serus finds it on data brokers and people-search sites and removes it.
Frequently asked
What does a web filter block?
Whatever its rules say: known malicious sites, categories such as gambling or adult content, or individual addresses a network owner has chosen to block.
Can a web filter see my browsing?
The system running the filter sees the addresses you request and can usually log them. Encrypted pages hide the content, not always the site name.
Can you bypass a web filter?
Sometimes, with a VPN or by changing DNS settings. On a work or school network that may break the rules, so check the policy first.
Sources
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