The report by Akamai Technologies Inc., based in Cambridge, Mass., says Indonesia's share of online attack traffic almost doubled from the first quarter to the second quarter of 2013, to 38 percent of reported global attacks, putting in ahead of China's 33 percent.
Indonesia was not on the list of top countries from which cyberattacks originated among the 175 countries or regions monitored by Akamai, during the last quarter of 2012.
Akama, in its report, acknowledged it only tracks attacks to IP addresses, which could have been hijacked by attackers in other countries.
"For example, a criminal in Russia may be launching attacks from compromised systems in China," Akamai said.
Developing countries like Indonesia often have growing but still insecure IT networks that hackers look for, it said.
Indonesia's population, the world's fourth-largest, and its fast-growing population of Internet users make it an attractive source for hackers, experts said.
"They'll go for wherever the largest number of exposed machines is located and use them as a platform to launch attacks," a report from technology media company IDGConnect said. "In the case of Indonesia ... it's a numbers game."