acp_logs.php, mcp_logs.php:

FIND

					$sql = 'DELETE FROM ' . LOG_TABLE . "
						WHERE log_type = {$this->log_type}
						$where_sql";
					$db->sql_query($sql);

REPLACE WITH

					$keywords = utf8_normalize_nfc(request_var('keywords', '', true));

					// Use no preg_quote for $keywords because this would lead to sole backslashes being added
					// We also use an OR connection here for spaces and the | string. Currently, regex is not supported for searching (but may come later).
					$keywords = preg_split('#[\s|]+#u', utf8_strtolower($keywords), 0, PREG_SPLIT_NO_EMPTY);
					$sql_keywords = '';

					if ($deleteall && !empty($keywords))
					{
						$keywords_pattern = array();

						// Build pattern and keywords...
						for ($i = 0, $num_keywords = sizeof($keywords); $i < $num_keywords; $i++)
						{
							$keywords_pattern[] = preg_quote($keywords[$i], '#');
							$keywords[$i] = $db->sql_like_expression($db->any_char . $keywords[$i] . $db->any_char);
						}

						$keywords_pattern = '#' . implode('|', $keywords_pattern) . '#ui';

						$operations = array();
						foreach ($user->lang as $key => $value)
						{
							if (substr($key, 0, 4) == 'LOG_' && preg_match($keywords_pattern, $value))
							{
								$operations[] = $key;
							}
						}

						$sql_keywords = ' AND (';
						if (!empty($operations))
						{
							$sql_keywords .= $db->sql_in_set('log_operation', $operations) . ' OR ';
						}
						$sql_keywords .= 'LOWER(log_data) ' . implode(' OR LOWER(log_data) ', $keywords) . ')';
					}

					$sql = 'DELETE FROM ' . LOG_TABLE . "
						WHERE log_type = {$this->log_type}
						$where_sql
						$sql_keywords";
					$db->sql_query($sql);