When 21-year-old Zhang, an average student in college, got set for the Graduate Record Exam (GRE) in Beijing this year, she felt so unprepared that she skipped the exam entirely.

Forty days later, she flew to Vietnam and nailed a near-perfect score in the test, which is taken by candidates applying to graduate school in the United States.

The secret to her sudden stroke of brilliance?

Before the second exam, Zhang -- not her real name -- tapped into an online network of former test-takers who pool questions and answers to gain an edge in the computerized test, which is not offered in China.

I heard from my friends that it is easier to get better grades in the computer-based exam, said Xu, another Chinese student who flew to the Philippines and came back with a score of 1420 out of 1600. Now I think it was money well-spent.

The coordinated cheating on the computerized GRE poses a challenge for the Princeton, New Jersey-based Educational Testing Service, which develops and administers the exam.

The stakes are high. On August 6, the computerized GRE will return to China after a nine-year hiatus, after ETS launches a revised GRE worldwide. That will allow much greater numbers of Chinese students to tap into online cheating networks if the revised GRE fails to curb their methods.

For Chinese, post-graduate study at a U.S. school is the ticket to prestige, adventure, and possibly higher wages.

ETS's Office of Testing Integrity closely monitors testing, investigates security issues and assures score validity worldwide for all ETS testing programs, Christine Betaneli, ETS spokeswomen for the GRE tests, wrote in an email to Reuters.

ETS takes test security very seriously and has a number of processes and procedures in place to ensure the highest standard of validity in testing. Some of our protocols are shared with the public, while some methods remain confidential.

The protocols outlined by Betaneli -- handwriting samples, photographs and voice matching -- would help deter one person from taking the test on behalf of someone else, but they would do little against the coordinated online cheating system.

ETS has instituted new security measures for the revised GRE. Betaneli did not elaborate, saying they were confidential.

COMPUTER EXPERIENCE

In a well-coordinated global effort, Chinese students who have just taken the computerized GRE load as many questions and answers as they can remember on to online chatrooms.

They call it ji jing, or computer experience. It capitalizes on a weakness in the testing system, namely that test organizers cannot introduce new questions fast enough to keep test-takers from finding out the questions in advance.

ETS painstakingly develops and evaluates each question, making it unlikely that the computerized test, offered weekly around the world, could contain unique questions each time.

The online system is more than just simple sharing. Blogs and forums on the Chinese search engine Baidu point potential test-takers toward chatrooms, staffed by volunteer organizers.

The organizer collates the contribution and posts an officially edited version of the questions with answers and analysis by the end of the day.

Those taking the test in Asia in the morning are responsible for the first three questions. Post them as quickly as you can, and those in the afternoon will benefit a lot! said one organizer in a blog post.

The contributors take the tests primarily in North America and Southeast Asia. New test-takers benefit from the time difference to memorize the responses posted from other continents.

FIVE MISTAKES

Some chatroom organizers worry about scores being too high.

We must follow the score-control strategy, admonishes one. Test-takers were advised to make five mistakes to ensure scores aren't so high that they expose the system.

In China, Hong Kong, Taiwan and South Korea the exam has only been offered in paper form since 2002, when ETS discovered websites containing GRE questions.

The websites included both questions and answers illegally obtained by test takers who memorize and reconstruct questions and share them with other test takers, ETS said in 2002. It decided to retire questions after each paper test, to prevent cheating.

An extensive investigation covering more than 40 countries showed security breaches occurring only in these areas.

Around the same time, ETS won a lawsuit in Chinese courts against the New Oriental Language School, a chain of schools that teach English and test preparation. New Oriental had published complete copies of previous tests, including questions that ETS re-used in subsequent years.

Despite the lawsuit, copies of those previous exams still can be found at sellers of pirated books in Chinese cities.

Teachers in test-preparation schools in China now advise students that to get better scores, they should take the computer-based GRE abroad, according to a student who attended one such class.

Some Chinese note that widespread sharing of questions casts suspicion on the scores earned by any Chinese student, whether or not that individual had cheated.

It's utterly unfair for Chinese students who work so hard for the test, said He Minghao, a 21-year-old who took the GRE test in June.

Shame on those who cheated. Their behavior discredits our hard-earned score as we are all Chinese students and their high scores give them an advantage over us in the application, especially when it comes to scholarship offers. Jijing should be forbidden.

(Reporting by Beijing newsroom; Writing by Lucy Hornby; Editing by Ken Wills and Alex Richardson)