Why Is My Website Blocked on Some Devices? How to Diagnose and Fix It

Why is a website blocked on some devices but not others?

Five common causes 

Several independent security layers can block access to a website, each operating according to its own rules. Understanding which layer is involved is the first step to fixing the problem. 

1. Antivirus and endpoint security software 

Products such as Kaspersky, Norton, and Bitdefender maintain databases of URLs they consider unsafe. If your domain was ever associated with spam, malware, or a shared hosting environment that was previously compromised, it may still appear on that list, even if you resolved the issue long ago. This is what is known as a false positive: your site is safe, but the security vendor's database has not been updated. 

2. Firewall and network restrictions 

Corporate, school, and government networks frequently apply content filtering rules. These rules may block entire categories of websites, specific domains, or certain types of content. A site that opens without issue on a home broadband connection may be completely inaccessible from an office network. This is particularly relevant if your target customers include enterprise buyers, procurement teams, or organisations in regulated industries. 

3. Browser security settings 

Browsers run safe-browsing checks before loading a page: Chrome and Safari both rely on Google’s Safe Browsing database, while Edge uses Microsoft Defender SmartScreen. If your domain triggers a warning in Google's Safe Browsing database, users will see a full-screen red warning before the page loads. These flags are not always up to date, and a domain can remain flagged for weeks after the underlying issue has been resolved. 

4. DNS filtering 

Some internet providers and network administrators use DNS-level filtering to block specific domains. A user on an affected connection cannot resolve your domain at all, regardless of whether your site is working perfectly. They will often see a generic connection error, though some filtering services display a branded block page identifying the filter instead. 

5. Cached blacklist data 

Outdated DNS records cached on a device can cause persistent blocking even after you have resolved the underlying issue. Flushing DNS on the device restores access in these cases. Note that browser safe-browsing warnings are not cleared; this way those lists update on the browser’s own schedule. This is the least common cause on the list, but the quickest to rule out.

Key term: What is a false positive in website security? 

A false positive in website security is when a security tool incorrectly identifies a safe website as harmful. It is common after a domain has been previously flagged, even briefly, because security vendors do not always update their databases promptly. Your site is fine; the database simply has not caught up. Most vendors process false positive submissions within a few business days, though timelines vary. 

How to investigate the problem 

Before attempting any fix, identify exactly where the block is coming from. A structured approach saves time and avoids making changes that have no effect

VirusTotal (virustotal.com) is the most useful first step. It is a free tool that scans your URL or domain against over 70 security vendors simultaneously. If any vendor has flagged your site, the results show which one and why. This takes under a minute and immediately narrows down where the problem lies. 

For businesses asking how ongoing website maintenance fits into their budget, our guide on Mobile App Maintenance Costs: What Every Business Should Know covers the responsibilities that come with running a live digital product, including security monitoring and DNS hygiene. 

How to fix a website that is blocked on some devices 

Once you have identified the source of the block, the resolution depends on which layer is causing it. 

Step 1: If antivirus software is blocking the site 

Most security vendors provide a false positive submission form on their website. Submitting your domain for review typically results in it being whitelisted within a few days. In the meantime, you can advise affected users to add your site to the allowed list in their antivirus settings, usually found under Network or Web Protection. 

Step 2: If a corporate or school network is blocking the site 

This is not something you can resolve directly. The affected user will need to contact their IT administrator and request that your domain is added to the network’s allowlist. If your prospects or clients are in enterprise or public sector organisations, it is worth flagging this proactively and offering an alternative contact route (such as email or phone) while they raise it internally. 

Step 3: If the browser is showing a safe-browsing warning 

Submit your domain for review via Google Search Console or directly through Google's Safe Browsing report tool. This covers both Chrome and Safari, as Safari’s Fraudulent Website Warning is powered by Google’s Safe Browsing database. Edge uses Microsoft Defender SmartScreen, which has its own “report an incorrectly flagged site” process on Microsoft’s website. Resolution typically takes a few days after passing review. 

Step 4: If DNS filtering is the cause 

First establish whether the problem is stale data or active filtering. If it is stale data, flushing the local DNS cache on the affected device resolves it immediately. If a filter is actively blocking the domain, flushing will not help, because the next lookup is simply blocked again. On a home or personal connection, switching to an alternative DNS resolver such as Google DNS or Cloudflare DNS can bypass ISP-level filtering. On a managed corporate network, this usually will not work, as external resolvers are commonly blocked; the request needs to go through the IT administrator, as in Step 2. 

Step 5: Re-test and allow time for propagation  

Once changes have been made, re-test across multiple devices and networks. Allow anywhere from 24 hours to several days for vendor database updates and DNS changes to propagate fully. 

What this means for your business 

A website that appears blocked is not simply a technical inconvenience. For startups and SMEs in particular, the commercial consequences can be significant and largely invisible. 

• Lost leads and revenue: A prospect who encounters a security warning is unlikely to proceed. The damage is silent: you receive no bounce notification, and the visitor will not usually report the issue. 

• Damaged credibility: Even a brief false positive can undermine trust, particularly if a potential client encounters a red warning screen on their first visit to your site. 

• Inconsistent user experience: When access depends on which device or network someone is using, it creates an unreliable experience that reflects poorly on the business. 

• Campaign risk: A false positive that coincides with a product launch, paid campaign, or press mention can significantly reduce return on investment. 

• B2B and enterprise sales friction: Enterprise buyers and procurement teams often operate heavily filtered networks. If your site cannot be reached from those environments, you may be removed from consideration before a conversation begins. If you are planning a digital product for enterprise clients, our article on 10 Questions Every Business Owner Asks Before Building a Digital Product covers how to avoid these infrastructure oversights from the outset. 

This type of access failure is not limited to smaller websites. The Barclays app outage in early 2025 demonstrated publicly how digital access failures, at any scale, can damage reputation and erode customer confidence within hours. The same principle applies to your website, just without the headlines. 

Monitoring your domain's reputation across security vendors is not a one-off task. Build it into your regular website maintenance routine, particularly after any change to your hosting provider, domain settings, or email infrastructure. 

Recommended: Periodic domain reputation checks 

Run a free scan of your domain at virustotal.com every few months, or whenever you change hosting provider or DNS configuration. Early detection prevents the issue from affecting live traffic for an extended period of time. 

Summary: How to fix a website blocked on some devices 

A blocked website is almost always a security configuration issue, not a fault with the site itself. The steps to resolve it are straightforward once you have identified the source: 

1. Test across multiple devices and networks to isolate the cause 

2. Scan your domain on VirusTotal to check whether any security vendors have flagged it 

3. Submit false positive reports to any vendors that have flagged your domain incorrectly 

4. Advise affected users to whitelist your site in their antivirus settings, or contact their IT administrator if a network firewall is involved 

5. Clear the browser cache and flush DNS on affected devices 

6. Re-test once changes have been made and allow a few days for vendor updates to propagate 

The issue is solvable. With a methodical approach, most cases are resolved within a few days. For more on how AI and automation are changing the way businesses protect and manage their digital assets, see our article on 3 Ways AI Can Save Your Business Thousands of Hours. 

Run a free scan of your domain at virustotal.com every few months, or whenever you change hosting provider or DNS configuration. Early detection prevents the issue from affecting live traffic for an extended period of time. 

Frequently Asked Questions 

Why is my website blocked on some devices but not others? 
The most common cause is antivirus or firewall software on the affected device flagging your domain as unsafe. This is often a false positive: your website is working correctly, but the security tool’s database is out of date. Testing on multiple devices and networks helps identify whether the issue is device-specific, network-specific, or related to a particular security product. 

What is a false positive on website security? 
A false positive in website security is when a security tool incorrectly identifies a safe website as harmful. It can happen if your domain was previously associated with spam or shared hosting that was compromised. The fix is to submit a false positive report to the relevant security vendor, which typically resolves within a few business days. 

How do I check if my website has been blocked by antivirus software? 
Use VirusTotal (virustotal.com) to scan your domain for free. It checks your URL against over 70 security vendors and shows immediately which, if any, have flagged your site and why. This is the quickest way to identify a false positive. 

What should I do if my website is blocked on corporate networks? 
Corporate network blocks are controlled by the organization's IT administrator, not by you as the website owner. Ask the affected user to raise a request with their IT team to add your domain to the network allowlist. In the meantime, offer an alternative contact route such as email or phone. 

Can a website appear blocked even if it is technically working? 
Yes. A website can be fully functional and still appear blocked to certain users. The block is applied by a security layer — such as antivirus software, a firewall, a DNS filter, or a browser warning — sitting between the user and your site. Resolving the issue requires identifying and addressing that specific layer, not the website itself. 

How long does it take to get a website removed from a security blacklist? 
48 to 72 hours Timelines vary by vendor: some process false positive submissions within a day or two, while others take a week or more. Google's Safe Browsing review can take a few days after you submit a request via Search Console. DNS cache updates typically propagate within 24 hours once a fix has been applied.