An Ancaster, Ont. man accused of helping Russian intelligence operatives conduct a massive hack of Yahoo email accounts in 2013 pleaded not guilty to all charges in a San Francisco courtroom on Wednesday.

One of his U.S. attorneys, Andrew Mancilla, told CP24 that Baratov pleaded not guilty to charges that if proven, could put Baratov behind bars for as much as 27.5 years.

Baratov, 22, is accused of helping three Russian nationals, at least one of whom remains employed with the Russian Federal Security Service, in a hack that compromised 500 million Yahoo email accounts in 2014.

Baratov himself is accused of compromising 80 of those accounts.

He was arrested at his home in March and waived his right to an extradition hearing in a Hamilton courtroom on Aug. 18. He was brought to San Francisco by U.S. Marshals a short time later.

He has remained in custody since his arrest, having been denied bail in Hamilton.

If convicted, U.S. authorities are seeking to seize funds from Baratov, as well as a grey Aston Martin DBS coupe he allegedly purchased with proceeds from the hack.

Also indicted in the alleged conspiracy are Dmitry Aleksandrovich Dokuchaev, 33, Igor Anatolyevich Sushchin, 43, and Alexsey Alexseyevich (Magg) Belan, 29.