How To Remain Logged In - The Infamous "Remember Me" Checkbox
Persistent Login Cookies ("remember me" functionality) are a danger zone; on the one hand, they are entirely as safe as conventional logins when users understand how to handle them; and on the other hand, they are an enormous security risk in the hands of most users, who use them on public computers, forget to log out, don't know what cookies are or how to delete them, etc.
Personally, I want my persistent logins for the web sites I visit on a regular basis, but I know how to handle them safely. If you are positive that your users know the same, you can use persistent logins with a clean conscience. If not - well, then you're more like me; subscribing to the philosophy that users who are careless with their login credentials brought it upon themselves if they get hacked. It's not like we go to our user's houses and tear off all those facepalm-inducing Post-It notes with passwords they have lined up on the edge of their monitors, either. If people are idiots, then let them eat idiot cake.
Of course, some systems can't afford to have any accounts hacked; for such systems, there is no way you can justify having persistent logins.
If you DO decide to implement persistent login cookies, this is how you do it:
First, follow Charles Miller's 'Best Practices' article Do not get tempted to follow the 'Improved' Best Practices linked at the end of his article. Sadly, the 'improvements' to the scheme are easily thwarted (all an attacker has to do when stealing the 'improved' cookie is remember to delete the old one. This will require the legitimate user to re-login, creating a new series identifier and leaving the stolen one valid).
And DO NOT STORE THE PERSISTENT LOGIN COOKIE (TOKEN) IN YOUR DATABASE, ONLY A HASH OF IT! The login token is Password Equivalent, so if an attacker got his hands on your database, he could use the tokens to log in to any account, just as if they were cleartext login-password combinations. Therefore, use strong salted hashing (bcrypt / phpass) when storing persistent login tokens.
I try to stick to system of ongoing entering passwords. Even at home. Doesn't always work, but I try. sometimes forget to turn off the "remember me". When bringing the matter to automatism - all will become much easier. By the way, at the same time trains the memory. Thanks for your tips