New evidence suggests that the overall similarity between 
human and chimp DNA may be as low as 70 percent.

For example, The Era of Chimp to Man is Over tells us that:
"Given the fact that the chimpanzee genome is at least 
10 percent larger overall than the human genome ..." 
the 98% assertion is simply inaccurate.

See Here and the Links below for more details

Does ... DNA similarity ... prove common ancestry?

Human-Chimp Genetic Similarity: Is Evolutionary Dogma Valid?

Common DNA Sequences: Evidence of Evolution or Efficient Design?

See also Here and scroll down to:

Greater than 98% ... similarity? Not any more