A Columbian computer expert has claimed he have single-handedly changed the results of major elections across Latin America for a decade, as part of an explosive new interview which throws open the region's "dark side of politics".

Andrés Sepúlveda told Bloomberg that he accepted huge amounts of money to hack and disrupt elections in favour of right-wing candidates in Colombia, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua and Panama for almost eight years. His confessions are so startling the Mexican government was forced into an immediate denial that president Enrique Peña Nieto's 2012 election campaign spied on its rivals.

Currently serving a 10-year jail sentence in his native Columbia for computer crime relating to the country's elections in 2014, the 31-year-old said: "My job was to do actions of dirty war and psychological operations, black propaganda, rumours – the whole dark side of politics that nobody knows exists but everyone can see."

His services, which started small in 2005 as petty acts of digital vandalism, did not come cheap. By the end he was running sophisticated operations in charge of dozens of other hackers stealing data and surveilling' leftist political rivals. His activities included installing bespoke malware onto rivals' computers in order to monitor phone and email communications, as well as stealing drafts of speeches, campaign schedules and confidential minutes of internal meetings. He also operated a "virtual army" of Twitter bots and sock puppets, which he would use to undermine opponents and create the illusion of popular support for his clients.

In the 2012 elections in Mexico, which returned Peña Nieto's right-wing government to power after a decade in the wilderness, he claims to have been given a $600,000 (£420,000) budget to sabotage Peña Nieto's two main oppositions.

Chillingly, he could even tailor his work to hamstring individuals. He claims to have set up fake Facebook accounts for gay men who would then publicly support a conservative Catholic candidate, while he used automated 3am campaign calls in a tight race in the race for the governorship of the Mexican state of Jalisco that falsely purported to come from Enrique Alfaro Ramírez, a left-wing candidate who went on to lose by a hair.

Sepúlveda claims that money was a secondary motive, and that his goal was explicitly political. Growing up hating Marxist Columbian militias, he wanted to bolster rightist candidates against what he describes as "dictatorships and socialist governments".

Many of the people named as clients in the article have issued outright denials. For his part Sepúlveda says he wanted to go public as he was living under the threat of death, and in the hope that he would win a lighter sentence on review.