---- Remove Long string with various symbols using .htaccess
phranque - 2:31 am on May 11, 2013 (gmt 0)
welcome to WebmasterWorld, mailhaz!
those strings look like they were originally percent-encoded so that special or reserved characters were encoded. this mean all '[' characters were encoded as '%5B', '>' characters were encoded as '%3E', '<' characters were encoded as '%3C', etc. the string was subsequently re-encoded so all the '%' signs were replaced with '%25'. then the string was encoded a third time so all the '%' signs were again replaced with '%25'. therefore a '<' in the original string eventually became '%25253E'.
it might be worth unencoding that query string to see if it means anything to you afterward.
in general the solution is to use a RewriteCond with the QUERY_STRING as the TestString to see if it exists: