Spark customers are being targeted in what is being described as a particularly authentic seeming email scam.

The emails falsely advise customers that their account has been accessed, and they should enter their login details.

Michelle Baguley from Spark's communications team says their call centre has been inundated since this morning, with calls to their security team up 20 percent from people with concerns.

She says the emails carry the Spark logo, tell customers their account has been accessed from another location, and ask for login details.

"This scam today does look quite authentic they have used the correct Spark logo and there aren't the usual type of grammatical errors you usually see with these scams."

Baguley says anyone who gets the email is advised not to click on it, and to delete it immediately.

"We wouldn't ever contact you to get you to verify your account in this way. Our security team are on to it."