WASHINGTON, D.C. - A warning about using Wi-Fi tonight, potential hackers may be using these hotspots to get into your laptop. Some even masquerade as free public Wi-Fi, but watch out-- it's likely a virus.

While it's tempting to log on especially when the Wi-Fi is free, computer experts say many Wi-Fi networks lack adequate security. In some cases hackers will "spoof" or "copy" a legitimate network, something called "the evil twin." It essentially tricks you into thinking its secure and it's not.

Wi-Fi hotspots are popping up all over cities in coffee shops, restaurants and airports.

"It's safe," Ebenezer Sam told FOX5 along King Street in Alexandria, where the city set up a free hotspot.

But it's not as safe as you might think.

"Wireless is invisible," said Tom Conklin, with AirTight Networks, a Wi-Fi security company.

In Alexandria, for example, when you check for wireless connections you will find more than a dozen networks, many including the city's hotspot are unsecured.

Computer experts say that's a red flag. Click on an unsecured network and the information starts flowing, sometimes from your computer to a hacker.

"The time you have your guard down at a busy airport during the holidays or a busy workday you're going to connect to something that isn't what you think it is. It could be a man in the middle, somebody spoofing an access point. They're collecting your data inbound and outbound from the internet," Conklin told FOX 5.

Airtight Networks tested 27 airports w