Somali pirates are becoming more brazen in their attacks on commercial and passenger ships off the coast of Africa, and — thanks to international law — there is little that can be done to stop them.

Pirates ... you just can't hang 'em anymore.

In the 18th century, the British government made a "great show of how wicked pirates were" by hanging them in public, said David Cordingly, author of "Under the Black Flag: The Romance and the Reality of Life Among the Pirates."

"Often their bodies were coated in tar and wrapped up in chains and then hung from a gallows at the entrance of a port or harbor," Cordingly said. "The idea was to make it seem that it wasn't a very good career option to become a pirate."

But now, three centuries later, pirates sail the high seas with near impunity — stealing, blackmailing and intimidating commercial ships. And it's not clear who can or should be the pirate police.

"The authorities have to be very careful with the law of the sea and United Nations charters," Cordingly said. "Nowadays you can't simply charge in with warships, blast the pirates and hang them on the waterfront."

An international fleet of warships, including American, British, Danish, Italian, Greek, French and Canadian ships, has moved into the waters off Somalia, where the International Maritime Bureau estimates 100 attacks have occurred this year.

But protecting the sea is difficult. On Sunday, pirates tried to attack a U.S. cruise ship, the MS Nautica, with over 1,000 people on board. The Nautica was able to outrun the pirates, but other ships have not been so lucky — like the Saudi oil tanker seized late last month with its crew and $100 million worth of oil.

"There are statements in international law that say pirates are the 'enemies of all mankind,' and that goes back to the 1600s," said Linda A. Malone, director of the human rights and national security law program at the William and Mary Law School in Virginia.

"It’s a form of terrorism, but it's not done for political reasons. It's done for financial gain, although those lines are starting to blur," Malone said. "It's one of the oldest international criminal law offenses."

Barry Hart Dubner, a law professor at Barry University in Florida who has written extensively on piracy, said that on the high seas, anyone can step up to battle the pirates.

"It gets trickier when you try to get them in territorial waters (within 7.5 miles of the coastline), because theoretically you need permission of the coastal state. But they can use any force they want because they're considered enemies of mankind," Dubner said.

Bringing weapons on board ships is "strongly discouraged" by the United Nations' International Maritime Organization, and experts agree that arming commercial crews is a bad idea.

"If you hire a company to do it or even arm your crew personnel, I think it would put them more at risk than if they weren't. If they start shooting … now you have an international incident," said Michael Lee, assistant vice president at Miami-based "non-lethal" security company McRoberts Maritime Security.

Having weapons on board isn't just a health and liability hazard, it also increases insurance costs "exponentially," Lee said. Armed guards cost between $1,000 and $1,500 a day.

"The problem is that most ship owners will not allow crews to carry weapons on board the ship. Most of these crews come from the Philippines and other areas and they're worried they'll kill each other. They're more worried about that than they are about piracy," Dubner said.

Since they don't carry weapons, ships have to resort to non-violent methods to ward off pirates. Among them are long-range acoustic devices that blast loud, irritating noises at them. "It’s the most annoying sound you've ever heard in your life — you literally cannot operate. It makes you nauseous," Lee said.

Other non-lethal methods include electric fences and hoses. Ships can spray pirates with water and knock them off their ladders into the ocean before they can climb on board.

But non-violence isn't always effective, as was proved last week when pirates struck the MS Biscaglia, a chemical tanker that is operated out of Singapore but flies a Liberian flag, in the Gulf of Aden.

In that hijacking, three guards from a British anti-lethal security company, Anti-Piracy Maritime Security Solutions (APMSS), were unable to fend off the pirates and threw threw themselves overboard to avoid capture.

The U.N. Security Council extended its authorization for countries to enter Somalia's territorial waters with advanced notice and to use "all necessary force" when combating piracy, the Associated Press reported on Tuesday.

American security firm Blackwater Worldwide, which protects American diplomats and congressmen in Iraq, announced in October that it was making its 183-foot ship, the McArthur, available to companies looking to hire security.

The company said it is available to escort merchant vessels in the Gulf of Aden and is outfitted with helicopters that can patrol ships rather than put armed guards on board the vessels.

"This recent attack over the weekend on a U.S. cruise ship really ups the ante, I think, because once the attacks are going beyond merchant ships or isolated attacks against small private ships and are directed against passenger vessels with civilians from many states, that's going to prod the international community into being even more proactive," said Malone.

Yet, nobody wants to take the pirates on board and be responsible for them, especially when they come from war-torn places like Somalia, and that restricts how effective law enforcement can be, Cordingly said.

"They can't just hand the pirates over to a country where they can claim asylum," he said. "It does get all very tricky. One has to say that everything at the moment seems to be on the pirates' side."