It was once an amazing plugin. Not any more.
News reports claim that the once popular All in One SEO plugin has been compromised and experts have found it vulnerable to hacking attacks.
Two privilege escalation vulnerabilities were discovered earlier this week that may affect any web site running it.
According to Securi,
If your site has multi users including subscribers, authors and non-admin users logging in to wp-admin (like many multi author blogs around), you are a risk.
Also, if you have open registration, you are at risk.
Here are some alternate plugins to All in One SEO plugin.
The best way to fix the situation is to update the plugin immediately or switch to a compatible SEO plugin like the alternatives mentioned above.
Keep in mind that you got to make sure your page title structure and other settings are exactly replicated while switching to the new plugin or things can get really messed up on the SERPs.