Throughout history, arms races between opposing forces have led to significant technological breakthroughs. Battles of the Middle Ages led to the invention of the crossbow. Wars in the 19th century spurred the development of the machine gun. The world wars and the Cold War created the atomic bomb, intercontinental missiles and the Internet. The weapons of the 21st century’s arms race are more likely to be virtual, top U.S. counterterrorism officials told a Senate hearing on November 15. The rising tide of cyber-attacks by foreign governments, activists and non-state actors is expected to overtake the threat of terrorism in the coming years.

According to The Guardian, the heads of the FBI, Department of Homeland Security and the National Counterterrorism Center testified that the likelihood of a terrorist attack on U.S. soil is lower than at any time before 2001 and that the threat was migrating online.

“[A] cyber attack perpetrated by nation states and violent extremist groups could be as destructive as the terrorist attack of 9/11,” then-U.S. Secretary of Defense Leon Panetta predicted in 2012.

Countries are scrambling to develop cyber-warfare capabilities and defenses. Bloomberg Business Week reports that the Chinese government has invested heavily in building up an army of hackers to spy on the U.S. and others. The attacks are estimated to cost the U.S. economy $300 billion per year.

“[China wages] a large-scale cyber espionage campaign… [and] has successfully targeted the networks of U.S. government and private organizations,” says the U.S.-China Economic and Security Review Commission in a report released to Congress on November 20. The report also said that the commission believed China was using cloud technology to conduct spying.

“U.S. officials have estimated that foreign intruders have stolen terabytes of data from military and defense company computers over the past decade, with the loss of intellectual property and competitiveness valued at more than $1 trillion,” writes The Chicago Tribune.

Attacks from China are not the only cause for concern. The U.S. government is also worried about domestic hackers, according to Reuters. On November 19, several cyber-security experts advised Congress to shut down the website due to security vulnerabilities. The healthcare enrollment website, which has suffered from technical issues since its rollout, and suffers from glitches that can allow criminals to obtain confidential person information from users.

Websites also face attacks from “hacktivists” like the group Anonymous, which routinely disables sites as an act of protest or to advance a social agenda. A recent FBI memo obtained by The Guardian details how hackers associated with Anonymous exploited security holes in Adobe software over a year ago to gain access to websites operated by U.S. government agencies.

“The majority of the intrusions have not yet been made publicly known,” the memo stated. “It is unknown exactly how many systems have been compromised, but it is a widespread problem that should be addressed.”

Officials are taking the breach seriously. Anonymous has interrupted service to prominent websites before. It temporarily disabled PayPal when the online payments service stopped processing donations to anti-secrecy site WikiLeaks.

In his 2013 State of the Union Address, President Obama acknowledged the reality of cyber attacks on the United States and the need to create defenses to safeguard valuable information before hackers gain the ability to cause even more serious damage.

“America must also face the rapidly growing threat from cyber-attacks,” Obama said. “We know hackers steal people’s identities and infiltrate private e-mail. We know foreign countries and companies swipe our corporate secrets. Now our enemies are also seeking the ability to sabotage our power grid, our financial institutions, and our air traffic control systems. We cannot look back years from now and wonder why we did nothing in the face of real threats to our security and our economy.”