Black squares appears randomly on screen

below i've pasted snippet of desktop squares appeared day. yesterday appeared different places in mail.
squares 14 x 14 pixels

guess it's graphics related issue how bad think is? , has had similar experiences? i've tried google didn't find anything.

computer: mba 2011 i7 4gb, 256gb, 3 months old used 2 of them due travelling.

 

attached files:

• 

  screendump.png

  file size:

  9.2 kb

  views:

  1,068

take in repair.

 

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