* You’ve heard of virus checkers and even web filters but what about firewalls? Chances are your school’s computers are well protected, but what about at home? Firewalls control what Internet traffic enters or leaves your computer and warn you if hackers are trying to gain access - some try to persuade you to download Trojan horse programs, which are hidden on your computer but may allow the hacker to steal passwords and files. New Windows and Mac operating systems come with a pre-installed firewall, but it’s worth investing in one from a specialist company. You don’t have to be paranoid to use a firewall and with companies like Symantec and McAfee selling them for around pound;30, they’re a sound investment.