The next time you are tempted to open a suspicious email from someone you don’t know, remember the horror story I am about to tell you. A simple mistake can lead to harassing calls by people who demand money, take remote possession of your computer (like a ghost), and then threaten to take your house away.

This story comes from a reader who wants to warn others. His and his girlfriend’s last names have been removed to protect them from embarrassment:

“My [girlfriend] Betty and I have just had a harrowing experience with computer fraud,” Peter O. told me in an email and on a phone call. “It all started about two weeks ago. Betty got an email message in her spam folder saying that she was hacked.”

Being the curious type, Betty opened the email.

“Two days later, she received a message from ‘Microsoft’ saying that she had been hacked and that she should call a specific number to clear the Trojan [virus] out,” Peter said. “She did and turned her computer over to a man with a [foreign] accent.”

The message, of course, wasn’t really from Microsoft.

The guy on the phone showed Betty what he said was the virus and offered to remove it for $200. Betty agreed. Then, the fraudster persuaded Betty to take a $700 five-year protection plan. “She agreed, gave her credit card number and was glad that she had her computer back,” Peter said.

But she didn’t really have her device back. And now the guy on the phone also had control of her credit card.

Peter continued with his story: “Two days later, she received another call from the same man, same accent. Figuring he’d found a sucker, the guy’s story changed this time.

“He told Betty that they had discovered a flaw in their server,” said Peter. The fraudster said he’d now fix Betty’s computer and return all the money she’d already paid.

“He asked if she had a cellphone and she said, ‘no.’ The only phone she had was the one they were on,” said Peter.

Huh? What was going on? She’d get her money back — could that be?

Next, the fraudster said that he accidentally sent Betty $10,900. What he wanted Betty to do was to keep the $900 she’d already paid and return the $10,000 sent by mistake.

“He wanted her to stay on the line until all the transactions were complete,” says Peter. “She was to go to her bank, get the $10,000 and mail it to him in Australia, via overnight United Parcel Service, no signature required.”

If the couple wasn’t suspicious yet, this would get them there. “She was to wrap the $10,000 in newspapers and put them in three boxes: one very small, one middle-sized and the third large,” said Peter.

The guy wanted them to declare on the Customs form that the contents were worth only $500 each. The guy on the phone said this was to avoid taxes. “He would only give her the mailing address once she had the money, and she was not to hang up her phone,” said Peter.

Betty suggested that he simply remove the $10,000 from her credit card. But the guy said he couldn’t do that.

Peter said, “I was getting upset listening to this, so I took Betty’s phone and told the … guy that he was a crook and that this was a scam.”

The mystery guy denied it “vigorously,” Peter said.

The couple went to the phone in their bedroom and called 911. The 911 operator told them to call 311. The 311 operator gave them the phone number of the Federal Trade Commission.

The FTC informed them it was a scam. Microsoft doesn’t make contact with customers like that.

Betty was still on the phone with the guy. She told him that her bank was closed because it was 4 p.m. and it wouldn’t allow her to take $10,000 out of a cash machine.

There were new instructions. “He looked up the address of an Apple store in her neighborhood and wanted her to go there and buy five $2,000 Apple [gift] cards and then report back to him,” Peter says.

Betty refused. The store was too far, she said.

The crook upped the ante. “He then told her that she had $50,000 credit in her credit card account and that he was going to withdraw all of it and bankrupt her,” said Peter. He even threatened to take her house, although there was no way he could do that — at least no way I can think of.

Eventually, the couple hung up, something they should have done at the beginning. The crook kept calling, but Peter and Betty wouldn’t pick up.

“However, now her computer was still attached to their computer and they were moving the mouse around by remote control,” Peter said. “Eventually, we regained control of her computer and deleted all the remote access codes that we could find.”

The next day, they went to the Citibank — which issued the credit card — and contested the $900 charge that the crook had made. Betty asked that her credit card be canceled and that she be given a new one.

“We felt much better when we left the bank,” Peter said.

The next day, they took the computer to Staples and its tech team fixed the machine, installed virus protection software and sold Betty a legitimate protection contract.

The phone calls continued. Betty picked up only one of them, and it was a woman at a seemingly legitimate company’s billing department. The caller denied that anyone at her firm would do anything like that. But Betty knew better. “Hopefully this is the end of this experience,” Peter said, although the credit card charge hasn’t yet been resolved.

The takeaway: Trust no one except your mother. Even then, ask to see her photo ID.