Acer spent a lot of time defending themselves from HP, who took them to court repeatedly in the past over various patent violations concerning their laptops. Earlier this year, they began fighting back, seeking support from the companies that supplied them with components.

They're going even further now, having decided to sue HP, taking the now largest PC vendor in the world to court in a counterclaim of patent infringement. Concerning five patents that HP sued them over earlier this year, Acer claims HP is the one at fault:

Acer denies the infringement allegations in court documents. It alleges it's HP who has infringed on patents issued to the Industrial Technology Research Institute, to which Acer possesses the rights.
The story doesn't end there, however, with Acer also pointing the finger at four other companies, including Wistron, who supply parts to them. As part of them supplying, they are obligated to protect Acer from claims such as HPs.