To make NCBI accessible to everyone, we monitor how well our web servers perform. Single-origin sources with high rates of access can degrade website performance. Hence, we may block IP addresses sending us high traffic. Users under the blocked IP address receive the Access Denied error message. The message does not imply maliciousness on your part. Below we list several situations that cause the Access Denied message. We follow with recommendations on addressing each situation.  

Why did you get Access Denied error message? 

One of the following can cause the Access Denied error message:

•   You scripted against our websites or otherwise caused high rates of access. NCBI blocked access from your IP address.
• Someone else working under the same IP address misused our site, and we blocked the IP address. This can happen in organizations where many people work on shared networks. 
•  You encountered the Access Denied message when your IP is not blocked. This can happen when:
  • You are using a proxy or a firewall that has a different IP address than your computer. It may be this alternate IP that we blocked. 
  •  NCBI blocked and then unblocked your IP address in the past. Your web browser or environment preserved the block in your cache. While you are no longer blocked, you continue receiving the error message.  

Excessive use - If you know of scripts and other processes causing high access rates

•  Shut down these processes immediately.
• Read the How to Access NCBI Data in Bulk article.
•  Write to Help Desk with the following:
  • Acknowledgment that you read and will follow the large-data retrieval guide.
  • The entire Access Denied message so that we can see the displayed IP address.
  • If you can, provide the HTTPS request sent to our servers.

We can then verify the information and remove the block. Understand that we will block your access again if you resume your activities.

If you have no knowledge of excessive use 

Within an organization:

•  Contact your system administrator. Ask them to check for excessive requests going to NCBI servers. They should ask the liable users to take the corrective actions as described above.
• Ask the IT staff to write to our Help Desk on behalf of all affected users. We can work with them to restore access.

NCBI can't restore your personal access if excessive use from your network continues.

Cache issues

• Close and restart your browser.
• Clear your cache and/or browser cookies.
• Research how to adjust/control the cache settings and protocols for your browser. Do the same for your non-browser environments. 

Proxies and firewalls 

•  Check the What is My IP? site from the affected computer. Compare the IP that you see with the one in the Access Denied message.
• Contact your local system administrator or internet service provider. They can provide you with information on how your network is set up.
•  Contact Help Desk and provide the following:
  • The entire Access Denied message so that we can see the displayed IP address.
  • The IP address from the What is My IP? site.
  • Other relevant information from the system administrator or internet service provider.