BE CAREFUL what you Google. This is the clear message after an incident this week when a New York couple had an unwelcome visit from counter-terrorism authorities.

Blogger and journalist Michele Catalano was Googling pressure cookers. She wanted a pressure cooker to cook quinoa, which is that South American grainy stuff you can buy in the health food section of the supermarket. It was a harmless Google search.

Meanwhile, her husband had been using the same computer to search for backpacks. He needed a backpack. Who doesn't need a new backpack from time to time? He, too, was doing a harmless Google search.

The couple's 20-year-old son was all over the computer too. After reading about the Boston bombings, he was clicking links about home-made bombs. It was harmless stuff, done purely out of curiosity.

But nothing is harmless is these days of terrorism and counter-terrorism. Not when it leads authorities to believe someone might be manufacturing a home-made bomb.

"My son's reading habits combined with my search for a pressure cooker and my husband's search for a backpack set off an alarm of sorts at the joint terrorism task force headquarters," Ms Catalano wrote.

"That's how I imagine it played out, anyhow. Lots of bells and whistles and a crowd of task force workers huddled around a computer screen looking at our Google history."

What happened next was, authorities swooped. They visited the couple's home at about 9 in the morning. It was real black ops stuff. Six dudes in three black SUVs pulled up and surrounded the house.

They knocked. The husband let them in. They searched. And after not too long, they left, convinced the couple's home was one of the 99 per cent of such cases where there was no threat.

And that was that. Except that isn't entirely that, because as many are asking today: how on earth does the government know what people are Googling?

That question has particular relevance today, given National Security Agency leaker Edward Snowden has just been granted temporary asylum in Russia. Mr Snowden revealed details of a US intelligence program which monitors internet activity.

Ms Catalano has since updated her blog saying: "We found out through the Suffolk Police Department that the searches involved also things my husband looked up at his old job. We were not made aware of this at the time of questioning and were led to believe it was solely from searches from within our house."

Meanwhile, US website The Atlantic Wire picked up Ms Catalano's story and tried to ascertain exactly which members of the "joint terrorism task force" (JTTF) visited the Catalano home. The FBI and local police authorities both told the site it wasn't them.

An FBI spokesperson also said "officers, agents, or other representatives of the JTTF did not visit that location".

Whichever secretive agency made the visit, it's safe to say they weren't foodies. When Ms Catalano's husband explained she was Googling pressure cookers in order to cook quinoa, they asked: "What the hell is quinoa?".

Read Michele Catalano's full blog here