NEVER NEVER download any attachments from strangers period! and always check attachments for virus before you open it even if it from your friend or relatives. Because once the file is sent trojan can get in file anytime before arrive to your inbox or anyone can trick you by send file to you using friend's email. I have seen that lot of times. Matters of fact one just happen to one of my friend which SHE did not sent email to them and she already post warning them not to open it as i suggest to her to do so. Even i know someone from that shitty chatroom (which some do know) try send me virus by using fake email address and using my nickname as attachment file name, SO i am not stupid and just delete it. So not all emails are safe include hotmail, yahoo, aol, or even private emails. Even the anti virus program would not be able to scan ALL virus some can get through randomly.
Best suggestion is never give out your email address in publicily or to strangers, only to your friends who you trust the most. For those who sign up for such as newsletter or apply though online, just be careful what you sign up because most of those kinds do send spams through email.
oh sooner an suggestion take to support service if you are not expert at fixing computers or take to anyone who YOU know that can fix computers such as reformat all that, because if you are try fix it yourself by take advices from someone online would be very VERY difficult to do so, because they cant see what wrong with your computer via online.