In the past two school years, 40 states detected potential cheating on standardized exams given to public school students in grades 3 to 12, according to a new report released by the Government Accountability Office.

Of those states, 33 confirmed at least one instance of cheating, and 32 states canceled or invalidated test results from individual students, schools or districts as a result of either suspected or confirmed cheating, the GAO found. The GAO collected data from the 2010-2011 and 2011-2012 academic years.

The findings come as large-scale cheating scandals play out in cities such as Atlanta, where 82 educators confessed to altering test scores in 30 schools, and cheating allegations continue to hover around Washington, D.C., and elsewhere.

A majority of states report using best practices to ensure test security, yet a significant number of education officials around the country told the GAO that they still feel their standardized tests are vulnerable to cheaters.

The GAO surveyed the states and relayed its findings to the U.S. Department of Education, which has given states more than $2 billion since 2002 to help them develop and administer standardized tests. Federal law requires all students in grades 3 through 8 to be tested annually in math and reading and at least once in grades 10 through 12. Students must also be tested in science at least once during grades 3 through 5, 6 through 9 and 10 through 12.

Standardized test results have taken on greater weight during the Obama administration, which has prodded states to tie teacher evaluations to student test scores.

As states increasingly administer tests on computers, the security risks posed by paper and pencil tests will be reduced, but will be replaced with new worries about hacking and other digital threats, the GAO said.

The study (PDF) can be found on the GAO Web site.