EXHIBIT 99.1

VASCO Provides Full-Year 2005 Guidance; Reaffirms Full-Year 2004 Guidance

Full-year 2005 revenue expected to increase 35-45% over 2004. Full-year 2005
gross profit and operating income, as a percentage of revenue, expected to range
from 60-65% and 15-20%, respectively.

OAKBROOK TERRACE, Illinois and BRUSSELS, Belgium - December 16, 2004 - VASCO
Data Security International, Inc. (Nasdaq: VDSI: www.vasco.com), a global
provider of enterprise-wide security products that support e-business and
e-commerce, today provided guidance for its full-year 2005 results. In addition,
VASCO reaffirmed its guidance for the full year 2004. VASCO's Senior Management
will discuss the guidance today at 10:00 am EST/16:00 pm CET.

VASCO expects its full-year 2005 revenue to grow 35% to 45% over full-year 2004
revenue. VASCO believes that its growth rate in 2005 will accelerate over its
growth rate in 2004 as a result of an increase in the size of the authentication
market, an increase in the size and strength of its distribution channel, an
increase in its customer base and an increase in its penetration of the retail
or consumer banking market, which will be reflected in a higher average order
size and a lower average selling price.

Consistent with the increase in average order size, VASCO expects its gross
profit as a percentage of revenue to be in the range of 60% to 65% and its
operating income as a percentage of revenue to be in the range of 15% to 20%.
Operating income as a percentage of revenue also reflects VASCO's plan to
continue to increase its investment in sales and marketing in order to expand
the market's awareness of both the benefits from stronger authentication and
VASCO's capabilities to provide state-of-the-art strong authentication.

VASCO reaffirms its full-year 2004 guidance, which includes revenue growth of
23% to 27% over full-year 2003, gross profit as a percentage of revenue of 65%
to 69% and operating income as a percentage of revenue of 17% to 20%.

Within the context of the full-year 2004 guidance, VASCO expects that full-year
2004 earnings per fully-diluted common share will range from $0.09 to $0.10 per
share.

VASCO believes that, as expected, the fourth quarter of 2004 results will
reflect an increase in the revenue growth rate over 2003 with lower gross profit
and operating margins than in prior quarters of 2004. VASCO expects that the
fourth quarter results will include significant shipments related to larger
orders and reflect higher operating expenses primarily related to its increased
investment in sales and marketing and the continued strengthening of the Euro.
VASCO expects that fourth quarter 2004 earnings per fully-diluted common share
will range from $0.01 to $0.02 per share.

"We believe that VASCO's growth rate will accelerate in 2005 reflecting the
markets' increasing awareness of the need for strong authentication and the
increasing recognition of the strength of VASCO's product offering," said Ken
Hunt, VASCO's Chairman and CEO. "Over the last two years, VASCO has successfully
executed its turnaround plan and demonstrated its ability to achieve
double-digit growth. From that success, we were able to increase our investment
in sales and marketing in the second half of 2004 and increase the markets'
awareness of our capabilities, especially related to large-scale deployment of
authentication tokens to the retail or consumer level. We look forward to
continuing our investment, increasing the markets' awareness of our
capabilities, and establishing a strong growth rate for the foreseeable future."

Today, at 10:00 am EST/16.00 CET VASCO will hold a conference call, which will
be streamed on the VASCO website (www.vasco.com). Dial-in telephone numbers for
the conference call:
Dial-in US: 888-424-5801
Dial-in International: +1 973-409-9258



ABOUT VASCO: VASCO designs, develops, markets and supports patented "Identity
Authentication" products for e-business and e-commerce. VASCO's Identity
Authentication software is delivered via its Digipass hardware and software
security products. For user access control, VASCO's VACMAN products guarantee
that only designated Digipass users get access to the application. With over
12,5 million Digipass products sold and ordered, VASCO has established itself as
a world-leader for strong Identity Authentication with over 300 international
financial institutions and approximately 1,400 blue-chip corporations and
governments located in more than 80 countries.

Forward Looking Statements

Statements made in this news release that relate to future plans, events or
performances are forward-looking statements. Any statement containing words such
as "believes," "anticipates," "plans," "expects," and similar words, is
forward-looking, and these statements involve risks and uncertainties and are
based on current expectations. Consequently, actual results could differ
materially from the expectations expressed in these forward-looking statements.
Reference is made to the Company's public filings with the US Securities and
Exchange Commission for further information regarding the Company and its
operations.

For more information contact:
Jochem Binst, +32 2 456 9810, jbinst@vasco.com
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