Someone phones you claiming to be from Microsoft, or an antivirus company, or some random tech support facility. They claim their systems have detected that your computer is infected. And of course they are offering to help. So much so, that for just a one-time payment of X, they are willing to offer a full LIFETIME of guaranteed support.
Ah, but there's a catch. Actually, 4 catches.
1. The scammers generally want you to download a remote access service (usually pointing you to ammyy.com or logmein) and grant them access. This effectively gives the scammers full, unfettered control of your PC - and remember, these are criminals.
2. The scammers want you to install a certain antivirus. Unfortunately, the antivirus they sell you and install is usually counterfeit or just a trial version. That means it will either expire or the license will be revoked. Which leaves you sitting with non-functioning, useless protection.
3. The scammers recommend the latest Windows version. Also likely to be counterfeit. Non-genuine versions of Windows cannot be updated with the latest security patches. This means you now have an unsafe version of Windows to accompany that crippled antivirus you also purchased from the scammers. A double dose of risk.
4. So now the criminals that were given unfettered access to your PC (which easily could have allowed them to install a backdoor trojan), have left you with non-functioning antivirus and an operating system that can't be patched. That means if they did drop a trojan to your system (likely), your antivirus won't detect it and your operating system will be extra vulnerable to any further malware they want to deliver.
If you are contacted by one of these scammers, just hang up the phone. If you've already been victimized, here's what you should do.
1. Dispute the charges with your credit card provider. If the credit card companies get enough complaints and chargeback requests, they can (and will) close the merchant account and blacklist the company. This makes it harder - and far more expensive - for the scammers to stay in business. The only way to stop a scammer is to remove their funding source.
2. If you purchased a new version of Windows from the scammers, contact Microsoft customer service or run the genuine Microsoft validation tool. Do NOT leave the software installed if it's not valid. You won't be able to get any security updates for it, which means you will be at far greater risk of malware infection or computer intrusion. You should also consider contacting Microsoft customer service for assistance.
3. Antivirus or any other software purchased from the scammers should be discarded - the chances of it being counterfeit or trojaned are just too high.
4. If the scammers were given remote access to your computer, you should backup your data files, reformat the hard drive, and reinstall. Skipping this step could leave you with a trojaned system that can leave you vulnerable to bank account theft, credit card fraud, or other financial or computer theft crimes.
The worse thing you can do is to do nothing. At the very least contact your credit card company and dispute the charge. Stopping the revenue stream is the best way to put scammers out of business.