user23: Evaluating 200M positions per second and having a search tree of 20+ moves might not be enough to beat a World Champion if a computer searches in the wrong direction or if it's evaluating positions a human opponent would never consider (either by instinct and/or reasoning). Coding tactics is easy, coding strategy is hard.
Was Deep Blue human assisted when it beat Kasparov in 1997? Is there any evidence about that?
Can a commercial software chess game running on a "common machine" beat a chess master nowadays?

user11748: Kasparov did just (beginning of 2017) publish a new book on this topic. He comments on the whole IBM fair play issue in the book.
In the book Kasparov also reflects on why IBM placed Russian speaking security guards at his hotel and why a specific change was made to Deep Blue on the very same morning that the final game was to be played. And exactly a game play change related to the very opening that Kasparov had discussed with his team about the night before the final game.
Se also:
http://www.kasparov.com/deep-thinking-ai/

user109: Kasparov accused Deep Blue of cheating, but I don't believe there is any evidence about this.
Anything can happen on any day, so yes, a commercial software chess game running on a "common machine" can beat a chess master.

user70: It isn't hard to find machines/programs rated 2200+ nowadays, so yes machines can beat masters. 
Kasparov's comments versus Deep Blue are sour grapes.  Kasparov once boasted that a machine could not beat him because he could create and a machine could not.  He failed to realize that sufficiently deep tactics are indistinguishable from creation ;-)

user264: Game Over: Kasparov and the Machine is a decent enough documentary on the subject. The coverage does kind of imply that Kasparov was grasping at straws a bit. Like a typical World championship match there was a lot of behind the scenes tactics going on from both sides.
My feeling is that you only have to look at the ascent of Anand and other chess players who rely heavily on computers in their training and analysis to realise that, at the time of this match, there was a paradigm shift from human to computer as the dominant chess player.
Addendum:
There's a interesting tidbit in Nate Silver's “The Signal and the Noise: Why So Many Predictions Fail—But Some Don’t.” In it he describes an interview with one of the engineers who worked on Deep Blue:

Nevertheless, there were some bugs in Deep Blue’s inventory: not many,
  but a few. Toward the end of my interview with him, [Murray] Campbell
  somewhat mischievously referred to an incident that had occurred
  toward the end of the first game in their 1997 match with Kasparov. “A
  bug occurred in the game and it may have made Kasparov misunderstand
  the capabilities of Deep Blue,” Campbell told me. “He didn’t come up
  with the theory that the move it played was a bug.” The bug had arisen
  on the forty-fourth move of their first game against Kasparov; unable
  to select a move, the program had defaulted to a last-resort fail-safe
  in which it picked a play completely at random. The bug had been
  inconsequential, coming late in the game in a position that had
  already been lost; Campbell and team repaired it the next day. “We had
  seen it once before, in a test game played earlier in 1997, and
  thought that it was fixed,” he told me. “Unfortunately there was one
  case that we had missed.” In fact, the bug was anything but
  unfortunate for Deep Blue: it was likely what allowed the computer to
  beat Kasparov. In the popular recounting of Kasparov’s match against
  Deep Blue, it was the second game in which his problems
  originated—when he had made the almost unprecedented error of
  forfeiting a position that he could probably have drawn. But what had
  inspired Kasparov to commit this mistake? His anxiety over Deep Blue’s
  forty-fourth move in the first game—the move in which the computer had
  moved its rook for no apparent purpose. Kasparov had concluded that
  the counterintuitive play must be a sign of superior intelligence. He
  had never considered that it was simply a bug.


23: <p>Evaluating 200M positions per second and having a search tree of 20+ moves might not be enough to beat a World Champion if a computer searches in the wrong direction or if it's evaluating positions a human opponent would never consider (either by instinct and/or reasoning). Coding tactics is easy, coding strategy is <em>hard</em>.</p>

<p>Was Deep Blue human assisted when it beat Kasparov in 1997? Is there any evidence about that?</p>

<p>Can a commercial software chess game running on a "common machine" beat a chess master nowadays?</p>
 11748: <p>Kasparov did just (beginning of 2017) publish a new book on this topic. He comments on the whole IBM fair play issue in the book.</p>

<p>In the book Kasparov also reflects on why IBM placed Russian speaking security guards at his hotel and why a specific change was made to Deep Blue on the very same morning that the final game was to be played. And exactly a game play change related to the very opening that Kasparov had discussed with his team about the night before the final game.</p>

<p>Se also:<br>
<a href="http://www.kasparov.com/deep-thinking-ai/" rel="nofollow noreferrer">http://www.kasparov.com/deep-thinking-ai/</a></p>
 109: <p>Kasparov accused Deep Blue of cheating, but I don't believe there is any evidence about this.</p>

<p>Anything can happen on any day, so yes, a commercial software chess game running on a "common machine" can beat a chess master.</p>
 70: <p>It isn't hard to find machines/programs rated 2200+ nowadays, so yes machines can beat masters. </p>

<p>Kasparov's comments versus Deep Blue are sour grapes.  Kasparov once boasted that a machine could not beat him because he could create and a machine could not.  He failed to realize that sufficiently deep tactics are indistinguishable from creation ;-)</p>
 264: <p><a href="http://www.imdb.com/title/tt0379296/" rel="nofollow noreferrer">Game Over: Kasparov and the Machine</a> is a decent enough documentary on the subject. The coverage does kind of imply that Kasparov was grasping at straws a bit. Like a typical World championship match there was a lot of behind the scenes tactics going on from both sides.</p>

<p>My feeling is that you only have to look at the ascent of Anand and other chess players who rely heavily on computers in their training and analysis to realise that, at the time of this match, there was a paradigm shift from human to computer as the dominant chess player.</p>

<p>Addendum:</p>

<p>There's a interesting tidbit in Nate Silver's “The Signal and the Noise: Why So Many Predictions Fail—But Some Don’t.” In it he describes an interview with one of the engineers who worked on Deep Blue:</p>

<blockquote>
  <p>Nevertheless, there were some bugs in Deep Blue’s inventory: not many,
  but a few. Toward the end of my interview with him, [Murray] Campbell
  somewhat mischievously referred to an incident that had occurred
  toward the end of the first game in their 1997 match with Kasparov. “A
  bug occurred in the game and it may have made Kasparov misunderstand
  the capabilities of Deep Blue,” Campbell told me. “He didn’t come up
  with the theory that the move it played was a bug.” The bug had arisen
  on the forty-fourth move of their first game against Kasparov; unable
  to select a move, the program had defaulted to a last-resort fail-safe
  in which it picked a play completely at random. The bug had been
  inconsequential, coming late in the game in a position that had
  already been lost; Campbell and team repaired it the next day. “We had
  seen it once before, in a test game played earlier in 1997, and
  thought that it was fixed,” he told me. “Unfortunately there was one
  case that we had missed.” In fact, the bug was anything but
  unfortunate for Deep Blue: it was likely what allowed the computer to
  beat Kasparov. In the popular recounting of Kasparov’s match against
  Deep Blue, it was the second game in which his problems
  originated—when he had made the almost unprecedented error of
  forfeiting a position that he could probably have drawn. But what had
  inspired Kasparov to commit this mistake? His anxiety over Deep Blue’s
  forty-fourth move in the first game—the move in which the computer had
  moved its rook for no apparent purpose. Kasparov had concluded that
  the counterintuitive play must be a sign of superior intelligence. He
  had never considered that it was simply a bug.</p>
</blockquote>
