Pretending to be from the likes of Telstra, Microsoft or the NBN, scammers seem very convincing. They might know your name and address, plus they'll often back their claims with threats that your files may be lost forever if you don't act.

Some scammers are out to steal money or personal information. Others hope to charge you for fixing non-existent computer problems.

Jim turned off the notebook's Wi-Fi and shut it down, disconnecting from the internet so the scammers couldn't get back in even though they continued to call. Realising the computer couldn't be trusted, he turned to a tech-savvy friend for advice

Closer examination revealed two remote access tools surreptitiously installed on Gina's computer: TeamViewer and ConnectWise. They're legitimate applications, used by real help desk staff to take remote control of computers so they can fix real problems.

Unfortunately scammers can also use these applications to rummage through your computer, if they can trick you into installing them, says Chris Gatford – director at security testing specialist HackLabs.

"Once scammers have access to your computer they can wreak havoc – installing software, downloading your files and monitoring your keystrokes to steal passwords," Gatford says.

"Even worse, they can watch what you’re doing at any time, including activating your web camera and listening to everything you say."

Unfortunately antivirus software usually doesn't protect against this kind of scam, as you've been tricked into installing legitimate software.

Rather than simply uninstalling these applications, Jim's friend guided him through reverting his mum's computer to a previous System Restore point – rolling back time without affecting files in the My Documents folder.

"If you've fallen a victim to a scam like this I recommend having your computer checked by a local computer expert," Gatford says. "They might be able to restore from a system backup, or they might need to completely reinstall the operating system to be safe."

It's important to keep your guard up, as scammers can’t resist the temptation to come back for more, says HackLabs' practice manager Michael McKinnon.

"Scammers are really creative, dreaming up all sorts of stories to keep leeching money," McKinnon says. "They'll even claim to be from the FBI, insisting they've arrested the original scammers and need your credit card details to process your refund."

"When you pick up the phone these days, you need to be a lot more careful when it comes to trusting people."