Officials of the café on Elephant Road, from which the email was allegedly sent, told The Daily Star yesterday that they also provided shared connections to 23 nearby houses and offices and all of them use the same gateway.

Intelligence officials picked up Shaibal Saha Partha, a job-seeking graduate from an Indian university ,from the cyber café on charge of sending the email as a Hikmatul Zihad activist to Bangla daily The Prothom Alo.

Tens of millions of people actively use the Internet in more than 130 countries at any given time, but it is not easy for anyone to get lost in the crowd, as when someone online they leave traces behind.

There are more than one way to trace down an email sender. One of the basic ways is to look at the IP (Internet protocol) address -- a group of four numbers separated by dots like "134.243.50.17" used to identify the visitor.

Each e-mail carries bits of information in the message header and IP address is one of them. "Depending on one's Internet connection, the IP address can be different. The traced Static IP address was provided by Arin (American Registry for Internet Numbers), it is unique and has been assigned to a particular service provider," said Ahamed Bauani, manager, Internet Systems, Gonophone Bangladesh Limited, one of country's leading ISPs.

"It will however be different each time one gets hooked through a dialup connection, which is known as Dynamic IP address. In the case of a Private or fake IP address, assigned by the ISP, the address can vary," he added.

In case of the email in question, the National Security Intelligence (NSI) may have tracked the Static IP address (69.88.6.54) that was in the message header. US-based Hawaii Pacific Teleport, an Internet carrier company which is registered with Arin, provided this IP address to Global Technology Limited, a local Internet service provider (ISP) that, in turn, provided Heart.net with a shared broadband connection bearing a Private IP address in 172.16.0.5.

Technical experts of Global Technology told The Daily Star that the NSI experts went through their server's internal Connection- Tracking Log and traced the IP address assigned to Heart.net.

Any computer attached to the personal network of the café will bear this IP address and use the Static IP address as gateway. It means anyone can send the email from the café or from the 23 connections.

The café uses a Windows server and Network Address Translation (Nat) for routing and does not keep a Connection-Tracking Log, which means it is highly unlikely that the sender of the email can be traced.