Opening Write Protected Flash Disk

I found in the net there’s many flash disk protect error case and never solve. I found my friend flash disk was infected by certain virus, but when I want to delete it, there was a message telling that flash disk was locked. Almost all flash disk found in the market now coming without flash disk protected button, we know that, but how came this flash disk protected?

Don’t blame virus, maybe they aren’t related with this problem. One possible explanation, if you force me to blame the virus is, virus trying to write something on your disk, suddenly electricity goes off or you unplug your flash disk abruptly after knowing virus activity on your disk.