Need different temperature change data sets explained
There are several climate datasets around the world, two in America - NASA's GISTEMP, and NOAA's MLOST, and one in the UK - HadCRUT. These are the main datasets but there are others around the world, China, Japan etc.

The datasets differ slightly in the starting date, number of met stations included, degree of interpolation, and the way they get round the problem of lack of met stations in oceanic areas. 

As to being 'tampered with', this is a subtle malicious implication that the data has been fudged. It is also an insult to the scientific integrity of the thousands of climate scientists involved, whose aim, as in all of science, is to get at the truth. Of course, the data have been 'processed'. This is an essential part of data quality control to interpolate missing data, and to ensure consistency of the data set. But no data has been 'tampered with' in the sense of trying to lead to false conclusions.
One of the striking features of all the global datasets is that, despite minor differences, they all show the same basic characteristics of an accelerating global temperature - the 'hockey stick graph'. 

There is much dishonesty about, but not with the climate scientists. It is the climate skeptics who are being dishonest (not to mention scientifically incompetent).