NEWTON (CBS) – Boston-area cyclists beware: one rider says she made a disturbing discovery in a Newton bike lane.

Carrie Mosher says she found a handful of thumbtacks on a Winchester Street bike lane in Newton Tuesday morning.

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“Each one of the tacks in the bike lane was point up so someone took a lot of time and care to place them,” Mosher wrote on Facebook after cleaning up the tacks. “I just don’t understand.”

The organization Bike Newton warns this isn’t the first time. Back in April, more than 100 tacks were found in the bike path along this same street.

“It’s malicious,” says Scott Tambascio of Landry’s Bicycles. “That takes time out of your day. It’s incredible someone would go through that effort to lay them all up, especially facing up too.”

Landry’s customers were warning each other about the situation.

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“Today we had two customers come in,” Tambascio said Wednesday. “One was a victim of it; he needed flat fixes to be done on his bike.”

Alain Ferry was another victim this weekend in nearby Dover. He sees the tacks as an alarming sign of the times; Boston welcomes cyclists but many drivers don’t.

“We’ve got these old outdated roads that can barely support the vehicular traffic and now they’re getting modified to welcome cyclists and make cycling more safe,” Ferry said.

He says the tacks are no prank — but incredibly dangerous.

“It’s way more than a flat tire,” Ferry said. “It’s way more than slowing down a cyclist. It could potentially kill someone.”

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If you find tacks or other dangerous debris along bike paths in your area you’re encouraged to report it and remove the items if it’s safe for you to do so.