Social networking accounts for more than one-quarter of all time spent online, according to a new study by comScore.

Social networking was ranked as the top activity in Chile with 28.5% of total minutes and the second most popular activity in Argentina with 27.8% of total minutes according to the report.

In Argentina and Chile, Facebook maintained a its poupularity, reaching 9 out of 10 Internet users in January 2011.

The study revealed that in Argentina, portals account for the largest share of time spent online in January 2011 at 29%, but declined nearly 10 percentage points from the previous year, while social networking surged 12.6 percentage points to account for 27.8% of Argentinians’ total time online.

The Instant Messenger category was down by 6.6 percentage points to 19.6% of time spent and e-mail was down 2.1 percentage points to 7.1% of time spent.

In Chile, social networking ranked as the top online activity, accounting for 28.5% of total online minutes, up 8.9 percentage points from the previous year, as portals, Instant Messengers and e-mail all registered a decline in share of minutes.

Entertainment sites, which accounted for 10.9% of total minutes, gained 1.6 percentage points versus the previous year as online users continued to spend an increasing amount of time consuming entertainment content.

The research firm said that the in Argentina and Chile, Facebook was the most popular social networking destination.

In Argentina, 11.3 million visitors age 15+ visited Facebook from a home or work location, representing 88% of the Argentine online population.

In Chile, 6.5 million visitors (approximately 90% of the online population) visited Facebook in January 2011.

In Chile, Twitter reached 13.1% of all online users (nearly 1 million visitors) to rank 11th globally in terms of reach. In Argentina, the microblogging site reached 12.5% of all online users (1.6 million visitors), ranking 13th globally.

Fotolog and Windows Live Profile each ranked among the top 3 social networking sites in both markets, while Sonico, Badoo and Linkedin also held solid positions within the top ten.