source: https://www.securityfocus.com/bid/16269/info

BlogPHP is prone to an SQL injection vulnerability. This issue is due to a failure in the application to properly sanitize user-supplied input before using it in an SQL query.

Successful exploitation could result in a compromise of the application, disclosure or modification of data, or may permit an attacker to exploit vulnerabilities in the underlying database implementation. 

The following proof of concept is available:
http://www.example.com/index.php?act=login
username: a' or 1/*
password: anypassword