The California-headquartered firm said it received a total of 14,763 submissions in 2013, of which 687 bugs were found to be valid and eligible to receive rewards.
A bug is an error or defect in a software or hardware that causes a programme to malfunction. It often occurs due to conflicts in software when applications try to run in tandem.

The social networking platform, which has over 1.2 billion users globally, paid USD 1.5 million last year to security researchers who report bugs on its website.
"India contributed the largest number of valid bugs at 136, with an average reward of USD 1,353. The US reported 92 issues and averaged USD 2,272 in rewards," Facebook said in a post.

Brazil and the UK were third and fourth by volume, with 53 bugs and 40 bugs and average rewards of USD 3,792 and USD 2,950, respectively, it added.
Researchers in Russia earned the highest amount per report in 2013, receiving an average of USD 3,961 for 38 bugs, Facebook said.
“We have paid over USD 2 million since we got started in 2011, and in 2013 we paid out USD 1.5 million to 330 researchers across the globe,” Facebook said.

The average reward in 2013 was USD 2,204, and most bugs were discovered in non-core properties, such as websites operated by companies the firm had acquired, it added.
"2014 is looking good so far. The volume of high-severity issues is down, and we're hearing from researchers that it's tougher to find good bugs," Facebook said.
The social networking site said it will encourage best research in the most valuable areas and will continue to increase its reward amounts for high priority issues.