Regex to replace gibberish

Question

I have to clean some input from OCR which recognizes handwriting as gibberish. Any suggestions for a regex to clean out the random characters? Example:

---

Federal prosecutors on Monday charged a Miami man with the largest 
case of credit and debit card data theft ever in the United States, 
accusing the one-time government informant of swiping 130 million 
accounts on top of 40 million he stole previously.

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Gonzalez is a former informant for the U.S. Secret Service who helped 
the agency hunt hackers, authorities say. The agency later found out that 
he had also been working with criminals and feeding them information 
on ongoing investigations, even warning off at least one individual, 
according to authorities.

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Answer 1

One of the simpleset solutions(not involving regexpes):

#pseudopython

number_of_punct = sum([1 if c.ispunct() else 0 for c in line])

if number_of_punct >len(line)/2: line_is_garbage()

well. Or rude regexpish s/[!,'"@#~$%^& ]{5,}//g

Answer 2

A simple heuristic, similar to anonymous answer:

listA = [0,1,2..9, a,b,c..z, A,B,C,..Z , ...] // alphanumerical symbols
listB = [!@$%^&...] // other symbols

Na = number_of_alphanumeric_symbols( line )
Nb = number_of_other_symbols( line )

if Na/Nb <= garbage_ratio then
  // garbage