Illegitimate traffic has increased from 64% to 83% of incoming enterprise emails due to a tripling of directory harvest attacks by spammers to find valid email addresses.


According to a research by Tumbleweed, “Dark Traffic” or illegitimate traffic has increased from 64% to 83% of all enterprise emails received. The survey was done on a sampling of more than 100 million email messages.

According to Tumbleweed, “Dark Traffic” comprises of Directory Harvest Attacks (DHA), email Denial of Service (DoS) attacks, malformed SMTP packets, invalid recipient addresses, and other communication that are not related to valid email messages.

DHAs are attempts by spammers to find valid email addresses. The spammer connects to the company’s server and collects valid email addresses to send spam messages.

DoS attacks are an attempt to fill the email with spam messages so that legitimate emails are refused by the server.

John Thielens, CTO of Tumbleweed Communications, said, “In our first Dark Traffic Report in Q1 of 2005, we were genuinely surprised at the amount of hidden traffic flowing into the enterprise under the radar.

In compiling this latest Dark Traffic report, we were again surprised to see such large jumps in Directory Harvest Attacks and Denial of Service Attacks” [Source]

To view the complete research report, click here.

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