An Ottawa school was in lockdown earlier this week because of a gun reference posted on the social messaging service Yik Yak. And Charlottetown police said this week that some local students aren't attending school because they can't take reading the comments on Yik Yak.

The app has been linked to threats, pranks and cyberbullying at schools across North America, prompting many to block it.

But is that a good idea? Here's what you need to know about Yik Yak.

What is Yik Yak?

Yik Yak is a free mobile app that allows anyone to post public anonymous messages — not even a profile or password is required.

Unlike many similar apps, it's location-based, so the messages are targeted at those within 2.5 kilometres.

Yik Yak bills itself as an app that lets you "get a live feed of what everyone's saying around you."

Like many social messaging apps, it allows users to "upvote" or "downvote" messages they like or don't like.

What can it be used for?

Yik Yak has quickly grown popular in schools, where it can have positive uses such as sharing questions about homework.

Joel Westheimer, education columnist for CBC's Ottawa Morning, described one case in class where a student said he or she wasn't feeling well, asked if anyone had anti-nausea medication, and received a response from someone who was able to help.

The app has also been used in negative ways, however, raising serious concerns at some schools.

Why are schools concerned about Yik Yak?

In some cases, the app has been linked to problems such as threats, pranks and cyberbullying.

Yik Yak is a social media app that allows users to post anonymously within a 2.5-kilometre radius.

The lockdown at Hillcrest High School in Ottawa this week is among many across North America linked to Yik Yak. Similar incidents took place at two California high schools in November. In the U.S., charges were laid against 11 college students last fall for threats posted on Yik Yak in relation to eight different universities.

The app has also been used to encourage dangerous pranks at Ottawa schools such as pulling fire alarms.

Schools are also concerned about the app's use in cyberbullying. Recently, All Saints Catholic High School in Ottawa sent a note home to parents saying it and other schools "are experiencing an increased number of issues with respect to negative comments made on social media sites" such as Yik Yak.

Nima Naimi, who conducts cyberbullying research at McGill University in Montreal, says the anonymity offered by the app may lead to a lack of empathy and users saying things that they wouldn't normally say in person.

"That's the danger that causes cyberbullying to happen," he told CBC News in an interview last fall.

How have schools responded?

Some schools, such as Ottawa's All Saints Catholic High School, have sent notes home to parents about the app. That school and many others have also sought to block the app on school grounds.

Because the app is location-based, it can be blocked by geofencing.

In the U.S., Yik Yak partnered with a company called Maponics, a company that has GPS data for about 85 per cent of middle and high schools, in order to block the app on school grounds.

Some schools in Canada, such as Chilliwack Secondary School in B.C., have also blocked the app.

What is the downside of blocking the app?

Jones said one student expressed disappointment because of the potential positive uses of the app.

Westheimer adds that, in a way, blocking the app is futile.

"We all know this is a game of whack-a-mole. Does it make sense to block one app? I mean, there will be 10 more where they were."

What should parents and teachers be doing instead?

Westheimer says schools need to teach kids how to interact with each other in healthy ways, instead of just focusing on academics.

Rick Jones, principal of Chilliwack Secondary School, told CBC Radio's Spark that his school, in addition to blocking the app, is trying to encourage students to engage in responsible behaviour. He wants them to report inappropriate comments to Yik Yak or to teachers and to have them deleted.

Naimi suggested parents should also talk to their children about the fact that Yik Yak may not be as anonymous as it looks — in the U.S., the company has worked with law enforcement to get a number of students arrested for posting threats.

CBC Technology columnist Dan Misener said that if parents want to have an informed and meaningful conversation with their kids about Yik Yak, they should use it themselves.

"Download it, try it, poke around, see how it works, see the kinds of things that are being posted," he suggested. "And that's just going to help you have a better understanding and open up a dialogue with kids."