Analysis of Email Fraud and Phishing Attacks in May Reveal that 95% Contain Forged 'From' Addresses.

REDWOOD CITY, Calif. -- Anti-Phishing Working Group Report Concludes That Email Authentication is a Critical Component in the Fight Against Phishing

Tumbleweed(R) Communications Corp. (Nasdaq:TMWD) and the Anti-Phishing Working Group today released the "Phishing Attack Trends Report" for May 2004, an analysis of phishing scam attacks submitted to www.anti-phishing.org, the Internet's most comprehensive archive of email fraud and phishing attacks. While this analysis shows that the numbers of unique attacks grew by only 6% in May, it also reveals that over 95% of attacks rely on the use of forged 'from' addresses to hide the identity of the scammers and evade spam filters. This trend underscores the utility of email sender authentication technologies as a critical step toward reducing the effectiveness of phishing campaigns by preventing fraudulent emails from reaching inboxes.

Several email authentication standards have been proposed by members of the Anti-Phishing Working Group, and while the specifics vary, each aims to prevent messages with forged addresses from reaching email users. Once deployed by ISPs, email authentication promises to reduce the number of phishing attacks reaching inboxes, with the added bonus of stopping most spam and the majority of e-mail based worms and viruses.

Phishing attacks use 'spoofed' e-mails and fraudulent websites to fool recipients into divulging personal financial data such as credit card numbers, account usernames and passwords, social security numbers, etc. By hijacking the trusted brands of well-known banks, online retailers, ISPs and credit card companies, phishers are able to convince up to 5% of recipients to respond to them. The result of these scams is that consumers suffer credit card fraud, identity theft, and financial loss.

In May, there were 1197 new, unique phishing attacks reported to the Anti-Phishing Working Group. This was a relatively minor 6% increase over the number of attacks reported in April (1125). The average number of phishing attacks per day in May was 38.6 (up slightly from the 37.5 per day for April). Analyzing this information on a weekly basis shows two weeks that averaged over 300 attacks, but a significant dip during the week of May 29. This dip may be due to the Labor Day holiday in the U.S., and a resultant reduction in reported phishing attacks. Highlights the Anti-Phishing Working Group's May report include:

--95% of phishing and email fraud attacks used spoofed or forged 'from' addresses.

--The company most-targeted by phishing attacks in May was Citibank with 370 unique attacks. This is down from 475 in April.

--Attacks against U.S. Bank surged 170%.

--Attacks against AOL doubled.

--The most-targeted industry sector was Financial Services with 848 unique attacks.

For more information and analysis, please download a copy of the "Phishing Attack Trends Report" for May 2004 free of charge at http://www.antiphishing.org/APWG_Phishing_Attack_Report-May2004.pdf.

"One Achilles heel of phishing, and other related e-mail threats like spam and viruses, is the reliance on forged 'from' addresses to hide the sender's identity," said Dave Jevans, Chairman of the Anti-Phishing Working Group and Senior Vice President at Tumbleweed Communications. "The problem is that for the most part, email servers haven't cared where an email message claims to be from -- they'll accept anything. Once ISPs start to verify the source of messages, a lot of the bad things in email, including phishing, will be greatly reduced. Not many scammers will use their personal email accounts to launch a crime wave."

About the Anti-Phishing Working Group

The Anti-Phishing Working Group (APWG) is focused on eliminating the problem of phishing and email spoofing attacks, by developing and sharing information about the problem, and promoting the visibility and adoption of industry solutions. Membership in the group is open to qualified financial institutions, corporations, law enforcement agencies, public policy groups and solution vendors.

The Web site of the Anti-Phishing Working Group is www.antiphishing.org. It serves as a public and industry resource for information about the problem of phishing and email fraud, including identification and promotion of pragmatic technical solutions that can provide immediate protection and benefits against phishing attacks. The analysis, forensics, and archival of phishing attacks to the Web site are currently powered by Tumbleweed Communications' Message Protection Lab(TM).

About Tumbleweed Communications Corp.

Tumbleweed is a leading provider of secure Internet messaging software products for enterprises. By making Internet communications secure, reliable and automated, Tumbleweed's anti-spam, email firewall, secure file transfer, secure email, and identity validation solutions help customers significantly reduce the cost of doing business. Tumbleweed products are used by millions of end-users and tens of thousands of corporations. Tumbleweed customers include ABN Amro, Bank of America Securities, Catholic Healthcare West, JP Morgan Chase & Co., The Regence Group (Blue Cross/Blue Shield), St. Luke's Episcopal Healthcare System, the US Food and Drug Administration, and the US Navy and Marine Corps. Tumbleweed Communications was founded in 1993 and is headquartered in Redwood City, Calif. For additional information about Tumbleweed go to www.tumbleweed.com or call 650-216-2000.

SAFE HARBOR STATEMENT

Tumbleweed cautions that forward-looking statements contained in this press release are based on current plans and expectations, and that a number of factors could cause the actual results to differ materially from the guidance given at this time. These factors are described in the Safe Harbor statement below.

Except for the historical information contained herein, the matters discussed in this press release may constitute forward-looking statements that involve risks and uncertainties that could cause actual results to differ materially from those projected, particularly with respect to phishing techniques and patterns, as well as methods to combat phishing and other forms of email fraud. In some cases, forward-looking statements can be identified by terminology such as "may," "will," "should," "potential," "continue," "expects," "anticipates," "intends," "plans," "believes," "estimates," and similar expressions. For further cautions about the risks of investing in Tumbleweed, we refer you to the documents Tumbleweed files from time to time with the Securities and Exchange Commission, particularly Tumbleweed's Form 10-K filed March 15, 2004 and Form 10-Q filed May 10, 2004.

Tumbleweed assumes no obligation to update information contained in this press release, including for example its guidance regarding its future performance, which represents the Company's expectations only as of the date of this release and should not be viewed as a statement about the Company's expectations after such date. Although this release may remain available on the Company's website or elsewhere, its continued availability does not indicate that the Company is reaffirming or confirming any of the information contained herein.