Cyberwarfare
Definition: There is ongoing debate over how cyberwarfare should be defined and no absolute definition is widely agreed upon. While the majority of scholars, militaries, and governments use definitions that refer to state and state-sponsored actors, other definitions may include non-state actors, such as terrorist groups, companies, political or ideological extremist groups, hacktivists, and transnational criminal organizations depending on the context of the work.
Examples of definitions proposed by experts in the field are as follows.

'Cyberwarfare' is used in a broad context to denote interstate use of technological force within computer networks in which information is stored, shared, or communicated online.Raymond Charles Parks and David P. Duggan focused on analyzing cyberwarfare in terms of computer networks and pointed out that "Cyberwarfare is a combination of computer network attack and defense and special technical operations." According to this perspective, the notion of cyber warfare brings a new paradigm into military doctrine. Paulo Shakarian and colleagues put forward the following definition of "cyber war" in 2013, drawing on Clausewitz's definition of war: "War is the continuation of politics by other means":Cyber war is an extension of policy by actions taken in cyber space by state or nonstate actors that constitute a serious threat to a nation's security or are conducted in response to a perceived threat against a nation's security.
Taddeo offered the following definition in 2012:

The warfare grounded on certain uses of ICTs within an offensive or defensive military strategy endorsed by a state and aiming at the immediate disruption or control of the enemy's resources, and which is waged within the informational environment, with agents and targets ranging both on the physical and non-physical domains and whose level of violence may vary upon circumstances.
Robinson et al. proposed in 2015 that the intent of the attacker dictates whether an attack is warfare or not, defining cyber warfare as "the use of cyber attacks with a warfare-like intent."
In 2010, the former US National Coordinator for Security, Infrastructure Protection and Counter-terrorism, Richard A. Clarke, defined cyberwarfare as "actions by a nation-state to penetrate another nation's computers or networks for the purposes of causing damage or disruption". The target's own cyber-physical infrastructure may be used by the adversary in case of a cyber conflict, thus weaponizing it.

Controversy of term: There is debate on whether the term "cyber warfare" is accurate. In 2012, Eugene Kaspersky, founder of Kaspersky Lab, concluded that "cyberterrorism" is a more accurate term than "cyberwar." He states that "with today's attacks, you are clueless about who did it or when they will strike again. It's not cyber-war, but cyberterrorism." Howard Schmidt, former Cyber Security Coordinator in the Obama administration, said that "there is no cyberwar... I think that is a terrible metaphor and I think that is a terrible concept. There are no winners in that environment."
Some experts take issue with the possible consequences linked to the warfare goal. In 2011, Ron Deibert, of Canada's Citizen Lab, warned of a "militarization of cyberspace", as militaristic responses may not be appropriate. However, to date, even serious cyber-attacks that have disrupted large parts of a nation's electrical grid (230,000 customers, Ukraine, 2015) or affected access to medical care, thus endangering life (UK National Health Service, WannaCry, 2017) have not led to military action.
In 2017, Oxford academic Lucas Kello proposed a new term, "Unpeace", to denote highly damaging cyber actions whose non-violent effects do not rise to the level of traditional war. Such actions are neither warlike nor peace-like. Although they are non-violent, and thus not acts of war, their damaging effects on the economy and society may be greater than those of some armed attacks. This term is closely related to the concept of the "grey zone", which came to prominence in 2017, describing hostile actions that fall below the traditional threshold of war. But as Kello explained, technological unpeace differs from the grey zone as the term is commonly used in that unpeace by definition is never overtly violent or fatal, whereas some grey-zone actions are violent, even if they are not acts of war.

Cyberwarfare vs. cyber war: The term "cyberwarfare" is distinct from the term "cyber war". Cyberwarfare includes techniques, tactics and procedures that may be involved in a cyber war, but the term does not imply scale, protraction or violence, which are typically associated with the term "war", which inherently refers to a large-scale action, typically over a protracted period of time, and may include objectives seeking to utilize violence or the aim to kill. A cyber war could accurately describe a protracted period of back-and-forth cyber attacks (including in combination with traditional military action) between warring states. To date, no such action is known to have occurred. Instead, armed forces have responded with tit-for-tat military cyber actions. For example, in June 2019, the United States launched a cyber attack against Iranian weapons systems in retaliation to the shooting down of a US drone in the Strait of Hormuz.

Cyberwarfare and cyber sanctions: In addition to retaliatory digital attacks, countries can respond to cyber attacks with cyber sanctions. Sometimes, it is not easy to detect the attacker, but suspicions may focus on a particular country or group of countries. In these cases, unilateral and multilateral economic sanctions can be used instead of cyberwarfare. For example, the United States has frequently imposed economic sanctions related to cyber attacks. Two Executive Orders issued during the Obama administration, EO 13694 of 2015 and EO 13757 of 2016, specifically focused on the implementation of the cyber sanctions. Subsequent US presidents have issued similar Executive Orders. The US Congress has also imposed cyber sanctions in response to cyberwarfare. For example, the Iran Cyber Sanctions Act of 2016 imposes sanctions on specific individuals responsible for cyber attacks.

Types of threat: 

Types of warfare: Cyber warfare can present a multitude of threats towards a nation. At the most basic level, cyber attacks can be used to support traditional warfare. For example, tampering with the operation of air defenses via cyber means in order to facilitate an air attack. Aside from these "hard" threats, cyber warfare can also contribute towards "soft" threats such as espionage and propaganda.
Eugene Kaspersky, founder of Kaspersky Lab, equates large-scale cyber weapons, such as Flame and NetTraveler which his company discovered, to biological weapons, claiming that in an interconnected world, they have the potential to be equally destructive.

Espionage: Traditional espionage is not an act of war, nor is cyber-espionage, and both are generally assumed to be ongoing between major powers. Despite this assumption, some incidents can cause serious tensions between nations, and are often described as "attacks". For example:

Massive spying by the US on many countries, revealed by Edward Snowden.
After the NSA's spying on Germany's Chancellor Angela Merkel was revealed, the Chancellor compared the NSA with the Stasi.
The NSA recording nearly every cell phone conversation in the Bahamas, without the Bahamian government's permission, and similar programs in Kenya, the Philippines, Mexico and Afghanistan.
The "Titan Rain" probes of American defense contractors computer systems since 2003.
The Office of Personnel Management data breach, in the US, widely attributed to China.
The security firm Area 1 published details of a breach that compromised one of the European Union's diplomatic communication channels for three years.
Out of all cyber attacks, 25% of them are espionage based.

Sabotage: Computers and satellites that coordinate other activities are vulnerable components of a system and could lead to the disruption of equipment. Compromise of military systems, such as C4ISTAR components that are responsible for orders and communications could lead to their interception or malicious replacement. Power, water, fuel, communications, and transportation infrastructure all may be vulnerable to disruption. According to Clarke, the civilian realm is also at risk, noting that the security breaches have already gone beyond stolen credit card numbers, and that potential targets can also include the electric power grid, trains, or the stock market.
In mid-July 2010, security experts discovered a malicious software program called Stuxnet that had infiltrated factory computers and had spread to plants around the world. It is considered "the first attack on critical industrial infrastructure that sits at the foundation of modern economies," notes The New York Times.
Stuxnet, while extremely effective in delaying Iran's nuclear program for the development of nuclear weaponry, came at a high cost. For the first time, it became clear that not only could cyber weapons be defensive but they could be offensive. The large decentralization and scale of cyberspace makes it extremely difficult to direct from a policy perspective. Non-state actors can play as large a part in the cyberwar space as state actors, which leads to dangerous, sometimes disastrous, consequences. Small groups of highly skilled malware developers are able to as effectively impact global politics and cyber warfare as large governmental agencies. A major aspect of this ability lies in the willingness of these groups to share their exploits and developments on the web as a form of arms proliferation. This allows lesser hackers to become more proficient in creating the large scale attacks that once only a small handful were skillful enough to manage.