(Reuters) - Three, one of Britain's biggest mobile phone companies, said on Thursday hackers had accessed its customer upgrade database after using employee logins.<div><a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=RrCiZPxf5Ho:Oy5Qdg9fnxQ:yIl2AUoC8zA"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?d=yIl2AUoC8zA" border="0" /></a> <a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=RrCiZPxf5Ho:Oy5Qdg9fnxQ:V_sGLiPBpWU"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?i=RrCiZPxf5Ho:Oy5Qdg9fnxQ:V_sGLiPBpWU" border="0" /></a> <a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=RrCiZPxf5Ho:Oy5Qdg9fnxQ:-BTjWOF_DHI"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?i=RrCiZPxf5Ho:Oy5Qdg9fnxQ:-BTjWOF_DHI" border="0" /></a></div><img src="http://feeds.feedburner.com/~r/reuters/technologyNews/~4/RrCiZPxf5Ho" height="1" width="1" alt="" />