When you’re on social media, it’s easy for online predators to pretend to be someone they’re not.

Police said online criminals are constantly changing their strategies to contact more victims, so they want parents to be on high alert.

People might think photos and messages sent through apps like Snapchat, where they disappear after a certain time, are gone forever, but police said that’s not true.

“There’s a lot of people out there that think whenever you have something on a cell phone, and you delete it, that it’s gone forever. Well, it’s not, and, thankfully, we have the technology to bring some of that information back and use it prosecute these criminals,” Sgt. Matthew Plummer from Altoona Police Department said.

A study conducted by the Pew Research Center found that 33 percent of teens are Facebook friends with other people they haven’t met in person. Another study out of the University of New Hampshire said 16 percent of teens considered meeting someone they’ve only talked to online.

“We’re still stressing not only Snpachat, but with all social media apps, and the internet, for parents to constantly be monitoring this stuff,” Sgt. Plummer said.

Altoona Police have a computer investigator who helps with cyber crime cases, but the decoding and investigation process take time. They said the best way to avoid being a victim online is knowing what to look out for.