Many holidaymakers had paid tens of thousands of pounds to go on the Sea Princess's 104-day world cruise, which started in Sydney, Australia.
But when a dusk-till-dawn "ban" on deck "fun" was put in place for more than a week and the vessel became a "ghost ship", nerves got the better of some.
Rumours of a potential terrorist plot began to spread as curtains and shutters were apparently closed and lights were dimmed or switched off each night.
Passengers are said to have speculated as to the reason behind the darkness and quietness - before the captain addressed the ship and shed some light on it.
Captain Gennaro Arma "apologised for alarming passengers," said Carolyne Jasinski, who was on the cruise liner as a guest speaker.
"However, the threat, he said, was real and the ship must be prepared for a pirate attack," she added, writing for news.com.au .
The "ban", which reportedly saw the end of deck parties, outdoor films and late-night outdoor swimming, remained in place for 10 days.
It is said to have been implemented as the massive vessel travelled across the Indian Ocean, the Arabian Sea, the Gulf of Aden and the Suez Canal.
In these areas, "the risk of piracy is higher", Carolyne wrote.
"Now I knew why they had been playing a documentary on our cabin TVs about piracy on the high seas," she added. "They were getting us ready for what was to come; gently reminding us that piracy is still a problem."
The media consultant said the ban on outdoor partying and entertainment no longer seemed like such an issue, with few complaints from passengers.
Nearly 2,000 people were on the world cruise, ending in Dubai, at the time.
As well as the dusk-till-dawn restrictions, the captain also reportedly told the holidaymakers they would have to take part in a so-called "pirate drill".
This compulsory drill apparently saw them sent back to their cabins so they could be counted by staff on the Sea Princess, operated by Princess Cruises.
Carolyne wrote that tourists were advised to sit on the floor and hold on to hand rails - in case the boat had to suddenly swerve away from pirate vessels.
She also said that that captain said they could outrun such boats - but that officers were on watch at all times to look out for pirates off the coast of Somalia.
The dates of the world cruise are unclear. MailOnline reports that some holidaymakers had paid more than $50,000 (around £38,500) for the trip.
A Princess Cruises spokeswoman told Mirror Online: "We do not discuss specific security procedures or equipment on our vessels.
"In addition to our normal ongoing security training, additional piracy specific training is conducted prior to any of our vessels entering areas of concern.
"Any measures aboard Sea Princess were simply taken out of an abundance caution and not in response to a specific threat."