Ages ago, when dinosaurs roamed the earth and I was in college, I went to a recruiting event for a company that collected and sold statistical data. They explained that they got the information by installing programs on people's computer 'in exchange for' providing free products like screen savers. When someone pointed out that sounded like spyware they assured us it was entirely legal since their terms and conditions document disclosed that downloading their free product would result in installing their data collection software.
I'd still consider that malware, regardless of whether it was legal, which made me wonder what the legal implications of such would be. What would happen if I wrote a virus scan and I listed this program as malware and recommended its deletion? This could lead to the program being deleted from many computers and thus a reduction of the program's data collection, which could translate to a loss of profits. Can the makers of this program sue me for loss of profits? Would I risk getting into some legal debate as to whether their 'legal' product constituted malware?