Description
When you try to search for any word using Cyrillic characters you either see all products on search results page or a DB error.
 
Solution
Download the regular expression update to work with different encodings:
http://www.viart.com/downloads/constants-4.0.7.zip
 
Further, extract 'constants.php' into 'includes' folder of your shop via FTP in BINARY mode replacing an existing file. Please do not forget to make a backup copy of the current file in case something goes wrong.