The Tachyon Cannon is a weapon that keys into the bio-signature of the target. It disrupts every individual cell with matching DNA in a certain radius, taking the target (or targets) apart on a sub-cellular level.
In a flashback during Malefactor, Grandpa Max tried to use it to destroy Malware, but instead the dangerously psychotic Galvanic Mechamorph absorbed the very powerful weapon and mutated even further, thus entering into his third form.
This weapon is normally a weapon of last resort. It could potentially attack those with similar DNA to the target even if they were not directly in its path; Max said that if Malware used it against him, he could destroy every human within a hundred miles because humans have "less than one percent variation" in their genetic makeup.
Tachyons are hypothetical faster than light particles, which are capable of travel backward through time.