- Assess what you're downloading. Are you downloading a file that enhances your Mozilla Firefox browser or are you downloading pornography? There's a much greater chance that the pornography is going to have a virus hidden in the download than the Mozilla download. What's the file? That's your first clue.
- Look over the site. It may seem superficial, but if you're downloading a file from a very basic site there's a higher chance that the site will have a virus hidden in its downloadable files than from a site that looks like it's been made from years of dedicated web designers.
- Consider who you are downloading the file from. Think about it logically, if you're downloading something from Windows, say, it's not likely that you're downloading a virus. What's the context? That's the key.
- Are there other people that have downloaded the file? If there's a forum attached to the site that has people saying they've downloaded said file and have not experienced any problems, chances are, you aren't going to be downloading a Trojan or worm.
- Look at the size of the file. If it's too small for what it is, it's junk.
- Watch out for executable files, such as '.exe', '.bat', '.pif', and '.scr'. If you download one of these you are, potentially, opening yourself up to anything on that file once you activate it. Try scanning it with a virus checker or any other software that is like it - just to be on the safe side. One common trick used by crackers is to have a 'double extension' such as '.gif.exe'. Said file is actually an .exe, not a .gif.
Tips
- Try to get yourself a decent anti-virus program on your computer. Norton, AVG and Avast! are all trusted sites with very effective programs that help clean up and/or protect your computer from the nasties that float around the internet. Even if you just get the free version, it's worth having a defense against a multitude of threats.
- Use your common sense - could it be simpler?
- If you don't know if you can trust the website, try doing a 'WHOIS' look-up. Type the name of the website on a WHOIS site and it will find you lots of details that help you decide whether you can trust your download.
- If you receive an E-mail from an unknown sender with a file attached, delete it immediately. That has 'virus' written all over it.
- Type the name of the file into a search engine such as Google or Yahoo! and see what problems or lack thereof other people have had!
Warnings
- If you're totally worried and don't know whether you should trust the file or not, don't. There's no point downloading something if you don't trust it.
- If you do accidentally download something suspicious, go to www.grisoft.com and download their anti spyware program. Then remove the suspicious software if it shows it's dangerous. Afterwords, go to www.zonealarm.com and download their firewall.
Source: http://www.wikihow.com/Know-when-It-Is-Safe-to-Download-Something