As part of his plea agreement in a New Jersey courtroom last month in connection with a series of cyber attacks, former Rutgers University computer science major Paras Jha was forced to forfeit his bitcoin account--estimated to be worth about $180,000 at the time it was seized.

Today, that bitcoin cache is valued at more than $1.3 million in U.S. dollars.

In September, the U.S. Attorney in Manhattan announced the forfeiture of $48.2 million in bitcoin in connection with a high-profile drug and money laundering scheme that operated on an underground on-line black market bazaar called the Silk Road. If they had waited a few more months, the exploding value of the bitcoin would have represented a $212 million.

And in Utah, U.S. attorneys prosecuting a multimillion-dollar drug-ring are seeking to quickly sell seized bitcoin that was worth less than $500,000 when Aaron Shamo was arrested a year ago, and has since soared in price to about $8.5 million.

Despite the volatility of bitcoin, so-called cyber currencies remain a key coin of the realm in computer crime. And as bitcoin values have gone into the stratosphere, the forfeiture of those funds by convicted offenders in some of those cases has generated major windfalls for the feds.

The U.S. Justice Department could not say how much money bitcoin forfeiture has brought in. Some forfeitures are subject to pending investigations and have yet to be sold off. But officials said there has been an increase in forfeiture actions.

Bitcoin, a digital currency created in 2009, is not tied to any country. They are purchased or sold through marketplaces called "bitcoin exchanges," and exist electronically in a virtual bank account known as a "digital wallet" that can reside on one's computer, or in the cloud. While each bitcoin transaction is recorded in a public log called a blockchain, the names or the buyers and sellers are not revealed.

The anonymity makes it difficult to trace.

A spokeswoman for the U.S. Marshals Service said its asset forfeiture division manages the sale of bitcoins once it has been ordered by the court. Proceeds are deposited into the Department of Justice's assets forfeiture fund or seized asset deposit fund, depending on the status of the case.

Jud Welle, the former lead cyber prosecutor in the U.S. Attorney's office in New Jersey, said bitcoin and other cyber currencies are becoming increasingly prevalent in forfeitures by law enforcement because criminals typically turn to the tools most useful to hide their activity.

"In past, we would only encounter it on the dark web or sophisticated computer crime," said Welle, now a managing director with Stroz Friedberg, a worldwide cybersecurity and risk management consulting firm.

He said the difficulty in tracing bitcoin transactions made it particularly attractive to hackers involved in ransomware attacks.

"Now it's becoming ubiquitous and people are re-purposing it for non-computer crimes. Part of the attraction is a lack of scrutiny," said Welle.

John D. Cohen, a former intelligence official at the U.S. Department of Homeland Security, said the law enforcement implications of the convergence that occurs in the physical world and in cyberspace is only beginning to be understood.

"As criminals continue to incorporate the use of bitcoin and other cyber-currencies into their illicit activities, law enforcement will need to re-evaluate enforcement and investigative protocols--especially from the aspect of detecting suspicious transactions to take that usage into account," said Cohen, a professor at the Rutgers School of Criminal Justice in Newark and a senior advisor at the Rutgers University Institute for Emergency Preparedness and Homeland Security.

At the same time, he questioned whether there existing laws need to be re-evaluated to ensure that the use of cyber currencies are covered by current statutes.

But just how secure those digital currencies are from the eyes of law enforcement remains a question, said Janne Lindqvist an assistant professor in the Department of Electrical and Computer Engineering at Rutgers University and an expert in bitcoin technology.

"While criminals are and have been using bitcoin to evade law enforcement, how well they are able to do that depends a lot of their operational security. We are seeing people caught all the time and their assets seized," observed Lindqvist.

While bitcoin transactions are anonymous, the transactional logs are publicly available and investigators have traced back deals through computer IP addresses.

Lindqvist said assuming that someone is buying something illegal with bitcoins, ultimately someone is going to be able to track that person's identity.

"It may work for you for a while," he said.

Ted Sherman may be reached at tsherman@njadvancemedia.com. Follow him on Twitter @TedShermanSL. Facebook: @TedSherman.reporter. Find NJ.com on Facebook.