Not legal advice but good sensible computer security advice...

Get a good antivirus software and a firewall. Use them. Scan frequently. Also get hold of an Adware/malware scanner. Some antivirus systems claim to do this but there are also specialist ones out there such as 'Adaware'.

A firewall *should* if used correctly prevent any changes being made to your computer without your consent. You should get a notification when anyone tries to do anything. In general, a commercial firewall is better than the free one you get with windows but read reviews of any you buy.

Adware/malware are small programs that usually get installed into your computer by webpages. Often they are harmless but they can also be quite malicious. They are often subtle enough to slip past antivirus software (though some do scan for them specifically now). The most inoccuous ones simply send your marketing preferences to the website (mainly so they can tailor advertising to you) but some can do nastier things and you are better off not having them at all. Regular scans with an adware scanner helps to reduce these. Note: Porn sites are absolutely rife with adware and viruses so you should maybe scan for both everytime you visit any porn sites.

Having said all this, the underage pictures story you describe sounds like an urban legend. Its possible he was already messing around with paedo sites and got hit by someone in that community or by a virus on one of those sites but I do not beleive in the police appearing 'just as the files appear on his computer'. Whether it is true or not, it is certainly going to be a rare occurence.

There are ways to get to know true facts about people. Look out for red flags - signs that something is not right - in your discussions with someone. Asking for money is a big one (for scams not underage). Apparent immaturity in language is another. If you are building what is intended to be a proper relationship with someone then do not feel embaressed about asking for some form of proof of age before you progress. Easiest way to do this is on webcam or by photograph but there are issues with that as well. However, each sending photos to each other, fully clothed, showing something in the photo that proves it was taken to order (rather than copied from the internet) is one way to do it. For example, a photo of the person holding a copy of a newspaper released on the day with the headline and date visible. And bear in mind that trust and lack of trust works both ways, you should be prepared to also prove your own credentials because you could equally be a Ghanian scam merchant or a prepubescent.

There are lots of discussions on this site which discuss first meeting protocols and I suggest you read them as well. Basics include: no play on first date, safe meeting place in public, chaperones present (either overtly or covertly), safe call used (arrange with a friend that you will call them at Xpm and if you don't they are to raise hell with the authorities) and so on.