IDENTITY theft and credit card fraud are among the potential risks confronting Kiama computer users, following an "epidemic" of scam-based malicious software attacks.
Technician Edwin Humphries owns and operates a Kiama computer business. He has been involved in the industry for nearly 25 years.
He said during the past six months he had noticed an "absolute epidemic" of malware (malicious software), usually hijacks and Trojans, affecting computers.
Browser hijacking is the unauthorised modification of a web browser's settings, usually replacing the home page or search engine.
Some browser hijacks were easy to remove, whereas others required significant searching and removal time.
Mr Humphries said those reporting issues spanned all ages and varying degrees of computer competency.
"People get sucked in by these scams," he said.
"Largely, it uses people's basic desire to trust others.
"Using people's virtues to trap them is something I find highly objectionable.
"In some cases I have to install Windows from scratch, as it has been so badly infected.
"To have fixed it would have cost more than to recover it."
Mr Humphries noticed a spike in this activity during the past six months. He currently fixes about 20 hijacked computers a month.
He said some hijacks weren't detectable using internet security products, such as those that tricked users into installing them.
Mr Humphries said free virus checkers were worth what you paid for them, and suggested installing a quality security package.
"A lot of it is about identity theft and credit card fraud . . . that's often the ultimate goal," Mr Humphries said.
"Some adware and hijacks are about trying to get click-through revenue for people who advertise with those companies.
"It slows down your computer, sometimes to the point of no longer being usable.
"Worst case scenario is the computer becomes useless, completely unbootable.
"A lot of people are being trapped, and pay a relatively large sum of money to get their computer back in order."
One customer, Kiama's Graham Harmer, recently experienced similar issues with his computer.
"Graham is not the least computer competent, or the most; he's pretty computer savvy," Mr Humphries said.
"He got caught with two computers."
Mr Harmer, 77, who has used computers for 20 years, said the unwary could face very real threats. He said he was stung by sites that appeared legitimate.
"You seem a little naive to be caught by them, but it's darn easy to be caught out," he said.
"I regularly change passwords and am aware of the care necessary with any financial transactions online.
"As a consequence I have never been defrauded in this respect. I also run anti-virus and firewall protection.
"Nevertheless, particularly in recent times, when using what appears to be authentic and trustworthy websites, it is easy to miss links for products or services, usually pre-ticked, which then take the user to unsafe sites, which then can rapidly corrupt the operating system."
Visit kiamaindependent.com.au for tips on protecting your computer from attacks.