ICQ.exe is ICQ. more information can be found here.
Quote: ICQ (short for 'I Seek You') is about creating simple, massively
popular ways to communicate online. From the first internet-wide
instant messaging service launched in 1996, ICQ is CNET's all time most popular download and was labeled the world's fastest growing community. Today, with over 150 million registered users, ICQ stands for messaging on any platform, incredible global reach, one of the largest and most active global communities, and by far the coolest way to find, meet people & connect.