The Your computer has been locked Ransomware is computer infection that prevents you from accessing your Windows desktop, files, or applications until you pay a $300 ransom to the malware developers. This ransomware pretends to be a lock screen placed on your computer by the Department of Justice, Department of Homeland Security, and the FBI that states child pornography was detected on your computer. It then proceeds to state that you will face a $250,000 fine imprisonment from 4 to 30 years unless you pay a fine in the amount of $300. In reality, this is just a computer infection and not a legitimate government message, so you should ignore anything that it requests you to do.
As explained in this great blog article and site, this infection will also check your web browser history to see if you accessed certain sites. If you have, it will include the list of matched web sites in the lock screen to further scare you into thinking that your activities have been monitored. Once again, this is just the infection accessing your browser history and you do not have to be concerned about it.