If your system is hacked, _using_ any password manager is insecure. Some password managers also have poor encryption, so even read-only access to your password

If your system is hacked, _using_ any password manager is insecure. Some password managers also have poor encryption, so even read-only access to your password database can be bad. KeePass (KeePassX in Linux) is one of the best, but a simple keylogger can get your "master password" when you enter it, and thus access to your password database. Nothing is absolutely secure, there are just degrees of relative safety.