China and Indonesia headed the list of 177 countries named as sources of Internet attacks, a security survey said Tuesday.

The survey from US security firm Akamai found China remained at the top of the list in the first quarter of 2013, but its share of all attacks dropped to 34 percent from 41 percent in the fourth quarter of 2012.

"This decline is likely related to Indonesia making a sudden appearance in the second place slot," said Akamai's Bill Brenner, noting that Indonesia's share of cyber attacks surged to 21 percent from just 0.7 percent in the prior quarter.

The United States was the third largest source, but its share dropped to 8.3 percent from 10 percent earlier.

The next largest sources of cyber attacks were Turkey (4.5 percent), Russia (2.7 percent), India (2.6 percent), Taiwan (2.5 percent), Brazil (2.2 percent), Romania (2.0 percent) and Hong Kong (1.6 percent).

"We find that nearly 68 percent originated in the Asia Pacific/Oceania region, up from 56 percent in the fourth quarter of 2012, likely due to the massive increase seen in Indonesia," Brenner said.

"Europe accounted for just under 19 percent, while North and South America originated just over 13 percent combined."

Akamai also noted a four percent increase in the global average connection speed -- to 3.1 megabits per second.

South Korea had the highest average connection speed at 14.2 Mbps and remained the country with the highest level of "high broadband" adoption, growing to 50 percent, the report said.

The report estimated more than 733 million unique Internet addresses from 243 countries or regions connected to the Akamai platform, an increase of 3.1 percent over the previous quarter and 10 percent year over year.

Since a single IP address can represent multiple individuals in some cases, Akamai estimated the total number of unique Web users connecting to its platform during the quarter to be well over one billion.