wp-admin/error_log collecting errors generated by Stop Spammers Spam Prevention

Yesterday, I ran a Wordfence scan of my website and it said I had what looks like malicious code in my wp-admin/error_log. Wordfence helped me identify that the code belongs to error messages originating from the stop-spammer-registrations-plugin.

Can you tell me why the following code is in my error log?

[28-Apr-2016 17:41:28 UTC] WordPress database error You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '')' at line 3 for query select option_id,option_value,option_name
from t68a5447_options where
INSTR(LCASE(option_value), 'eval(') +INSTR(LCASE(option_value), 'eval (') +INSTR(LCASE(option_value), 'networkads') +INSTR(LCASE(option_value), 'document.write(unescape(') +INSTR(LCASE(option_value), 'try{window.onload') +INSTR(LCASE(option_value), 'escape(document[') +INSTR(LCASE(option_value), 'escape(navigator[') +INSTR(LCASE(option_value), 'document.write(string.fromcharcode') +INSTR(LCASE(option_value), '(base64_decode') +INSTR(LCASE(option_value), '(gzinflate') +INSTR(LCASE(option_value), 'UA-27917097-1') +INSTR(LCASE(option_value), 'w.wpquery.o') +INSTR(LCASE(option_value), '<scr'+')  made by do_action('stop-spammers_page_ss_threat_scan'), call_user_func_array, kpg_ss_threat_scan, include_setting, require_once('/plugins/stop-spammer-registrations-plugin/settings/kpg_ss_threat_scan.php')

https://wordpress.org/plugins/stop-spammer-registrations-plugin/