Russian police are reportedly investigating a criminal gang that installed malicious "ransomware" programs on thousands of PCs and then forced victims to send SMS messages in order to unlock their PCs.

The scam has been ongoing and may have made Russian criminals millions of dollars, according to reports by Russian news agencies. Russian police seized computer equipment and detained a Russian "crime family" in connection with the crime, the ITAR-TASS News Agency reported Tuesday.

Russian-language reports say that 10 people are expected to be charged and that tens of thousands of Russian-language victims were hit by the scam, which also affected users in Ukraine, Belarus and Moldova.

The criminals reportedly used news sites to spread their malicious software, known as WinLock, which disables certain Windows components, rendering the PC unusable, and then displays pornographic images.

To unlock the code, victims must send SMS messages that cost between 300 rubles ($9.72) and 1,000 rubles.

The scam is "very popular" in countries such as Russia at the moment, antivirus vendor Kaspersky Lab said.

Security experts have tracked this type of software for more than a year now, but in most of the world it rarely shows up, according to Dave Marcus, director of McAfee Labs security research communications.

The software is not considered to be a very sophisticated threat, he said. "It's just locking your screen with a password you don't know, which is not that sophisticated when you get down to do."