Everybody downloads from the web. Softwares, games, and files... they could contain issues attached to them. When you attempt to download anything, make sure your security is working. That way you can prevent a lot of trouble.

I'll present here some hints in order to save you time and money looking for antivirus and anti-trojan, but remember, there's no 100% safe system, otherwise that would be the end of security issues worldwide forever.

1) Before you start navigating the web, make sure you have a FIREWALL, and make sure it's ON, and working properly;

2) When downloading anything from anywhere, make sure you download it from the ORIGINAL website or source. Don't go to any random site you find on your web search engine;

3) Use tools that make the hard work for you, but remember, don't trust them 100%; 

4) Don't accept files from unknown people when using messengers, e-mails, etc;

5) After downloading the file, verify it with your anti-virus;

6) Make sure your softwares are updated;

7) Make your regular anti-virus and anti-trojan detection schedule.

8) If you are away from keyboard, or even gone for a few days, turn the computer off, if possible;

It's not wise to leave it idling there, logged on the internet.