A resurrected al-Qaida has vowed to renew its efforts to bring terror to Europe and America. The Islamic State seems focused on seizing and holding territory in Iraq and Syria not attacking the West....yet. However, the number of IS foreign terrorists holding Western passports is estimated in the many hundreds and the most senior American cabinet officers have publicly warned that the threat of attacks against the homeland is imminent.

One terrorist scenario that is making the rounds is hitting well-populated targets. Sports stadia, shopping malls and other people magnets are among them. Interestingly, books and movies have long used these locales as venues for terror strikes. In 2002, two snipers terrorized the Washington beltway region arbitrarily shooting innocents from the trunk of their car.

So how about this scenario? Suppose scores of bombs were mailed or delivered to cabinet officials, Supreme Court justices, banks, billionaires and other celebrities and were exploded simultaneously. What might follow?

Would panic set in and would the public demand in the name of safety and security rolling back constitutional protections to prevent further attacks including the detention of thousands of possible perpetrators on preventative grounds? How long would such a reign of de facto martial law last? Would the Patriot Act be made even stronger and would the National Security Agency and police be empowered to intrude further on privacy and civil rights?

Actually, this scenario occurred 95 years ago. On May Day, 1919 some several dozen bombs were mailed to well-known Americans from Supreme Court associate justices to the attorney general and John D. Rockefeller. That January another round of attempted bombings occurred. The country also was laboring under the Espionage and Sedition Acts passed in 1917 and 1918 to give the government sweeping powers during World War I against German agents and anarchists.

The Attorney General, whose home was partially destroyed in the first bombing, was a Quaker, A. Mitchell Palmer. Palmer had declined Woodrow Wilson's offer of making him Secretary of War in 1915 on religious grounds. Later he accepted the position of attorney general. His executive assistant was twenty-something J. Edgar Hoover.

The country was roiling over riots, unemployment after the war and fear of red takeovers following the October Revolution of 1917 that left the Bolsheviks in charge of Russia. Bolsheviks and communists then were feared as more dangerous than al-Qaida and IS are today. Panic was an accurate description of the mood in America.

On the second anniversary of the Bolshevik Revolution in 1919 and in January 1920, Palmer struck with the so-called Palmer raids. Tens of thousands were arrested or detained without due process under the Sedition Act. And the country grew more fearful.

Several hundred anarchists were eventually deported to Russia aboard a Navy warship. But none of the perpetrators of the bombings were ever identified or convicted. Yet that period, long forgotten, was the first instance of how a terror gripped nation provoked massive intrusion on individual liberties and civil rights, the largest intrusion ever since the Civil War.

Could terrorists launch simultaneous massive attacks against public places such as stadia, malls, railway stations and airports? The answer is yes. Should government then be doing more to warn the nation about such contingencies? Or, without good intelligence and reliable evidence of specific plans for attacks, would such warnings do more harm than good?

These are profoundly perplexing questions. Any answer has benefits and downsides, most unpredictable. But this is the shape of things to come. And even more vulnerable and potentially more damaging targets are present.

Cyber attacks against financial institutions, credit cards and individual bank accounts are not only coming. They are here. Some attacks are simply hackers doing this for sport. More sinister is organized crime that is stealing billions through cyber attacks.

Obviously, IS and other terrorist organizations have the potential ability to carry out a full range of financially directed cyber attacks. Other cyber attacks such as those directed against Iranian centrifuges can be physically disabling. Power grids, telecommunications centers and other key infrastructure assets are highly vulnerable to and can be incapacitated by cyber attack.

How much should the public worry? All societies have frailties that can become vulnerabilities. Terrorist attacks can target them much as al-Qaida took down the Twin Towers.

Two conclusions are important. First, the nation is resilient and should never panic even if these types of terrorist attacks are launched. Second, civil liberties are vital. A repeat of the Palmer Raids of 1919 and 1920 would do far more damage to the nation than any terrorist attacks. A return to that time would be the worst form of terror.

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Harlan Ullman is Chairman of the Killowen Group that advises leaders of government and business and Senior Advisor at Washington D.C.'s Atlantic Council and Business Executives for National Security. His latest book, due out this fall is A Handful of Bullets: How the Murder of Archduke Franz Ferdinand Still Menaces The Peace.