Hyderabad, Nov. 6 -- Plenty of people use a free VPN to get around blocked websites or to stay safe on public Wi-Fi. But a notice issued by the US Federal Bureau of Investigation (FBI) earlier this year warns that some of these apps may quietly turn your phone or computer into part of a "residential proxy" network.

That lets strangers send their internet traffic through your connection. If the traffic is criminal, it can look as though you were behind it.

What is a residential proxy?

A residential proxy is a go-between. It lets someone use the internet through another person's connection, borrowing the IP address of an ordinary phone, computer, streaming box or home router. To the websites on the other end, the traffic looks like it is...