A Web bug is an object that is embedded in a web page or e-mail and is usually invisible to the user but allows checking that a user has viewed the page or e-mail. One common use is in e-mail tracking. Alternative names are Web beacon, tracking bug, tracking pixel, pixel tag, 1×1 gif, and clear gif.
A Web bug is any one of a number of techniques used to track who is reading a Web page or e-mail, when, and from what computer. They can also be used to see if an e-mail was read or forwarded to someone else, or if a Web page was copied to another Website. The first Web bugs were small images.
Some e-mails and Web pages are not wholly self-contained. They may refer to content on another server, rather than including the content directly. When an e-mail client or web browser prepares such an e-mail or Web page for display, it ordinarily sends a request to the server to send the additional content.
These requests typically include the IP address of the requesting computer, the time the content was requested, the type of Web browser that made the request, and the existence of cookies previously set by that server. The server can store all of this information, and associate it with a unique tracking token attached to the content request.
E-mail Web bugs
Web bugs embedded in e-mails have greater privacy implications than bugs embedded in Web pages. Typically, the URL of Web bugs contained in e-mail messages carry a unique identifier. This identifier is chosen when the e-mail is sent, and is recorded together with the recipient e-mail address. The later download of the URL signals that the e-mail has been read. The sender of the e-mail is therefore also able to record the exact time that a message was read, as well as the IP address of the computer used to read the mail or the proxy server that the user went through. In this way, the sender can gather detailed information about when, and from where, each particular recipient reads e-mail. Additionally, every time the e-mail message is displayed, another request may go to the sender's Web site.
Web bugs are used by e-mail marketers, spammers, and phishers to verify that e-mail addresses are valid, that the content of e-mails has made it past the spam filters, and that the e-mail is actually viewed by users. When the user reads the e-mail, the e-mail client requests the image, letting the sender know that the e-mail address is valid and that e-mail was viewed. The e-mail need not contain an advertisement or anything else related to the commercial activity of the sender. This makes detection of such e-mails harder for mail filters and users.
Tracking via Web bugs can be prevented by using e-mail clients that do not download images whose URLs are embedded in HTML e-mails. Many graphical e-mail clients can be configured to avoid accessing remote images. Examples include the Gmail, Yahoo!, and SpamCop/Horde webmail clients; Mozilla Thunderbird, Opera, Pegasus Mail, IncrediMail, later versions of Microsoft Outlook, and KMail mail readers. Other HTML techniques (such as IFrames) can still be used to track e-mail viewing.
A Web bug is any one of a number of techniques used to track who is reading a Web page or e-mail, when, and from what computer. They can also be used to see if an e-mail was read or forwarded to someone else, or if a Web page was copied to another Website. The first Web bugs were small images.
Some e-mails and Web pages are not wholly self-contained. They may refer to content on another server, rather than including the content directly. When an e-mail client or web browser prepares such an e-mail or Web page for display, it ordinarily sends a request to the server to send the additional content.
These requests typically include the IP address of the requesting computer, the time the content was requested, the type of Web browser that made the request, and the existence of cookies previously set by that server. The server can store all of this information, and associate it with a unique tracking token attached to the content request.
E-mail Web bugs
Web bugs embedded in e-mails have greater privacy implications than bugs embedded in Web pages. Typically, the URL of Web bugs contained in e-mail messages carry a unique identifier. This identifier is chosen when the e-mail is sent, and is recorded together with the recipient e-mail address. The later download of the URL signals that the e-mail has been read. The sender of the e-mail is therefore also able to record the exact time that a message was read, as well as the IP address of the computer used to read the mail or the proxy server that the user went through. In this way, the sender can gather detailed information about when, and from where, each particular recipient reads e-mail. Additionally, every time the e-mail message is displayed, another request may go to the sender's Web site.
Web bugs are used by e-mail marketers, spammers, and phishers to verify that e-mail addresses are valid, that the content of e-mails has made it past the spam filters, and that the e-mail is actually viewed by users. When the user reads the e-mail, the e-mail client requests the image, letting the sender know that the e-mail address is valid and that e-mail was viewed. The e-mail need not contain an advertisement or anything else related to the commercial activity of the sender. This makes detection of such e-mails harder for mail filters and users.
Tracking via Web bugs can be prevented by using e-mail clients that do not download images whose URLs are embedded in HTML e-mails. Many graphical e-mail clients can be configured to avoid accessing remote images. Examples include the Gmail, Yahoo!, and SpamCop/Horde webmail clients; Mozilla Thunderbird, Opera, Pegasus Mail, IncrediMail, later versions of Microsoft Outlook, and KMail mail readers. Other HTML techniques (such as IFrames) can still be used to track e-mail viewing.
