Watch out for this fellas. It locks your computer saying you are being fined for looking at porn under the social information act 2012, then demands £100 to unlock your computer. Very clever, as it has Metroplitan Police branding.
They then take your details and empty your account if you are a sucker and fall for it.
It can come through, ahem, er, 'Gentlemen's websites', or it can come through anything including Facebook. (I got it on the MENSA website you understand)
Cost me 30 sheets to get rid of it at my local repairer, who said they are getting about 5 a day in!