When you book a hotel room online, you expect that the rate you see is the rate you’ll pay, right?

To help make sure that’s the case, the FTC is sending warning letters to 22 online hotel reservation sites that may be violating the law by not including mandatory fees, which can add as much as $30 a night to your stay, in some of the prices they quote online.

The Federal Trade Commission cracked down on a massive international scam that tricked tens of thousands of computer users into believing their computers were riddled with malware and then paying the scammers hundreds of dollars to “fix” the problem.    

According to complaints filed by the FTC, the scammers called computer users and claimed to be affiliated with legitimate companies, including Dell, Microsoft, McAfee and Norton, and played on people’s fear of computer infections and hackers.