New evidence suggests that the overall similarity between 
human and chimp DNA is between 70-81 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

Journal Reports Bias in Human-Chimp studies

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