louisa,
not sure I would call it a "huge" sell off. It takes almost 20MM shares of volume to equal 1% of the float nowadays..:)
Secondly, I would venture a guess what ACT put in their 10K is part of what is going on..couple in reverse split talk etc
From ACT 10K:
1) We have issued approximately 126.2 million shares related to settlements during 2011
2) issued approximately 285.5 million shares on January 31, 2012 and February 7, 2012
3) We anticipate having to issue approximately an additional 135.5 million shares related to debenture settlements
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